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MODELLING AND CHARACTERIZATION

AA

Computations for materials – discovery, design and the role of data

The integration of theory, computation and data is transforming modern materials design and discovery. This symposium brings together global leaders in theory, computation and data driven materials research as well as renowned experimentalists to present and discuss the latest achievements in the field.

Scope:

The large-scale deployment of first-principles electronic structure calculations in combination with the ever-increasing power and availability of massively parallel supercomputers launched in the last couple of decades an entirely new paradigm in modern materials science. Intuition and serendipity that were the hallmarks of materials discovery and design are now complemented by computationally guided searches and collaborative theory-experiment efforts. Furthermore, availability of the data that is generated in the process generates unprecedented opportunities to further advance and accelerate design and discovery of novel materials at a scale that has not been seen before.

The main goal of this symposium is to gather leading scientists and engineers from academia, national labs and industry to discuss the status and the outlook for research and applications of computation and data driven materials science, with an emphasis on the experimental validation and the integration of theory, computations and experiment. The common challenges and opportunities will be at the focus of the discussions. The symposium will cover a wide range of studies including advancements in theory, computational methods (including high-throughput), the role of data in modern materials science, and materials synthesis and characterization for accelerated design and discovery.

Hot topics to be covered by the symposium:

  • Materials design and discovery
  • Designing magnetism and strongly correlated systems
  • Metastability and metastable materials
  • Materials thermodynamics and thermochemistry
  • Defects, doping and transport
  • Structure predictions, applications and recent advancements
  • The role of data: data mining and machine learning
  • The role of data: the Rise of experimental databases
  • Modeling of interfaces
  • Materials synthesis and characterization for accelerated design and discovery

List of invited speakers:

  • Axel Gross, Ulm University, Germany
  • Artem Oganov, Skolkovo Institute of Science and Technology, Russia
  • Fumiyasu Oba, Tokyo Institute of Technology, Japan
  • Kristian S. Thygesen, Technical University of Denmark
  • Stefano Sanvito, Trinity College, Dublin, Ireland
  • Thomas Olsen, Technical University of Denmark
  • Oleg Yazyev, EPFL, Switzerland
  • Kristian Haule, Rutgers University, USA
  • Andriy Zakutayev, NREL, USA
  • Eric Toberer, Colorado School of Mines, USA
  • Tonio Buonassisi, MIT, USA
  • Alfred Ludwig, University of Bochum, Germany
  • Rampi Ramprasad, Georgia Tech, USA
  • Luca Ghiringhelli, Fritz-Haber-Institut of the Max Planck Society, Berlin, Germany
  • George E. Froudakis, University of Crete, Grece

Publication:

Selected papers will be published as a focus issue of the journals, JPhys Materials and JPhys Energy (IOP Publishing).

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Accelerated materials discovery : -
09:15
Authors : Artem R. Oganov
Affiliations : Skolkovo Institute of Science and Technology, 3 Nobel St., 121205 Moscow, Russia

Resume : In the last 10-15 years, a number of approaches made it possible to discover new materials on the computer prior to experimental verification. This holds a transformative potential for the development of new technologies. A special role in this development is played by our evolutionary algorithm USPEX, developed by me and my students since 2004. The methodology will be reviewed along with applications to several problems of materials science. To enable discovery of technologically useful materials, we implement multiobjective (Pareto) optimization and apply it to a variety of problems: Our new method, Mendelevian Search, capable of finding the best materials among all possible compounds with all possible crystal structures, will be described and illustrated by several results. I will describe results of our recent works along several lines: 1. Search for novel thermoelectric materials, where we show the possibility of achieving the figure of merit ZT>>1. 2. Discovery of novel superhard materials, holding promise to replace currently used materials. 3. Prediction of new high-temperature superconductors, approaching room-temperature superconductivity. 4. Prediction of novel chemistry of nanoparticles and possible explanation of carcinogenicity of oxide dust. Current limitations and future prospects of these methods will be discussed.

AA.1.1
09:45
Authors : Kamal Choudhary
Affiliations : NIST, Maryland, USA

Resume : JARVIS (Joint Automated Repository for Various Integrated Simulations) is a unique integrated framework to accelerate material design using classical force-fields (FF), density functional theory (DFT) and machine learning (ML). The JARVIS-DFT hosts data for more than 30000 materials. We discovered more than 1500 2D materials using lattice parameter criteria and exfoliation energy calculations. We charted improved lattice parameters, formation energies and elastic tensors using van der Waals functional for more than 12000 materials and established relation between exfoliation energies and elastic constants. To alleviate bandgap underestimation in conventional DFT and improve frequency dependent dielectric function predictions, we evaluated meta-GGA based approaches for more than 15000 materials. We use spectroscopic limited maximum efficiency approach to identify potential photovoltaic materials. Using spin-orbit spillage criteria, we discovered more than 1500 potential topological materials including topological insulators, Weyl and Dirac semimetals, and topological crystalline insulators. The database is publicly available at https://jarvis.nist.gov/.

AA.1.2
10:00 Coffee break    
 
2D materials : -
10:30
Authors : Kristian Thygesen
Affiliations : Technical University of Denmark, Department of Physics

Resume : I will introduce The Computational 2D Materials Database (C2DB) -- a new platform for modeling and discovering atomically thin crystals and their heterostructures [Haastrup et al., 2D Materials 5, 042002 (2018)]. The C2DB organises a variety of structural, thermodynamic, elastic, electronic, magnetic, and optical properties of around 3500 different 2D materials distributed over more than 40 different crystal structures. Materials stability and properties are systematically calculated by state-of-the-art density functional theory and many-body perturbation theory (GW and the Bethe–Salpeter equation for the simpler materials) following a semi-automated workflow for maximal consistency and transparency. The C2DB is fully open and can be browsed online (http://c2db.fysik.dtu.dk) or downloaded in its entirety. I will show how the we utilised the database to design novel Janus structures for predictive tuning of band alignment at heterointerfaces, new 2D semiconductors with high mobilities and strong light-matter coupling, and materials with non-trivial topologies.

AA.2.1
11:00
Authors : Wenhao Sun1*, Christopher Bartel2, Elisabetta Arca3, Sage Bauers3, Bethany Matthews4, Bernardo Orvañanos5, Bor-Rong Chen,6 Michael F. Toney,6 Laura T. Schelhas,6 William Tumas3, Janet Tate,4 Andriy Zakutayev3, Stephan Lany3, Aaron Holder2,3*, Gerbrand Ceder1,7
Affiliations : 1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA; 2 Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, USA; 3 National Renewable Energy Laboratory, Golden, Colorado 80401, USA; 4 Department of Physics, Oregon State University, Corvallis, Oregon 97331, USA; 5 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; 6 SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.; 7 Department of Materials Science and Engineering, UC Berkeley, Berkeley, California 94720, USA

Resume : Exploratory synthesis in novel chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation—from which we experimentally realized 7 new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity, and covalency of solid-state bonding from the DFT-computed electron density, we reveal the complex interplay between chemistry, composition, and electronic structure in governing large-scale stability trends in ternary nitride materials. An interactive version of the map can be found at https://wenhaosun.github.io/TernaryNitridesMap.html

AA.2.2
11:15
Authors : Yuan Ping Feng (1,2), Jun Zhou (1), Lei Shen (3), and Miguel Dias Costa (2)
Affiliations : (1) Department of Physics, National University of Singapore, Singapore; (2) Centre for Advanced Two-Dimensional Materials, National University of Singapore, Singapore; (3) Department of Mechanical Engineering, National University of Singapore, Singapore

Resume : Two-dimensional (2D) materials have attracted tremendous amount of interest. Their unique properties are expected to lead to new technologies. In an effort of systematic 2D materials discovery, we have been using both the top-down and the bottom-up approaches to generate 2D structures. On one hand, monolayer structures are theoretically exfoliated from layered three-dimensional structures. On the other hand, chemical elements in known 2D materials are systematically substituted by similar elements to generate new 2D materials. High throughput first-principles calculations are carried out to study their physical properties. Our progress in this project will be reported and some preliminary applications, such as bilayer heterostructures for excitonic solar cell applications, of the 2D materials database will be discussed.

AA.2.3
11:30
Authors : Adrien Stoliaroff, Camille Latouche, Stéphane Jobic
Affiliations : Institut des Matériaux Jean Rouxel

Resume : There has been an ongoing controversy on 1T-TiS2’s semimetallic1,2 or semiconducting nature3 for several decades due to the difficulty to synthetize stoichiometric TiS2 and the dispersion of calculation results. We tackle this issue by performing calculations on the CdI2 layered structure type with the ideal 1:2 Ti:S stoichiometry using some of the most refined models, e.g. hybrid functional including Grimme’s dispersion effects, the GW scheme and the Bethe-Salpether equation for the optical properties. All the calculations on the bulk (ideal) structure demonstrate that a (small) bandgap exists for the ideal material. Besides, van der Waals interactions must be taken into account during the calculation in order to reproduce accurately the TiS2 structure, more precisely a correct c/a ratio. Then, for the first time we study point defects in the material using the same level of accuracy. These calculations demonstrate unambiguously that the most stable defect is the titanium interstitial located in an octahedral site inside the van der Waals gap. This point defect may explain the distinguishable electronic behavior of TiS2 reported in the literature, i.e. non degenerated semiconductor (SC) or semimetal (SM) depending on defect concentration as a result of the synthesis conditions. (1) Liu, B.; Yang, J.; Liu, C.; Hu, T.; Han, Y.; Gao, C. The Ground Electronic State of TiS2: Experimental and Theoretical Studies. Phys. Status Solidi Curr. Top. Solid State Phys. 2011. https://doi.org/10.1002/pssc.201000612. (2) Thompson, A. H.; Pisharody, K. R.; Koehler, R. F. Experimental Study of the Solid SolutionsTixTa1-xS2. Phys. Rev. Lett. 1972, 29 (3), 163–166. https://doi.org/10.1103/physrevlett.29.163. (3) Logothetis, E. M.; Kaiser, W. J.; Kukkonen, C. A.; Faile, S. P.; Colella, R.; Gambold, J. Transport Properties and the Semiconducting Nature of TiS2. Phys. B+C 1980, 99 (1–4), 193–198. https://doi.org/10.1016/0378-4363(80)90231-4. (4) Stoliaroff, A.; Jobic S.; Latouche, C. Optoelectronic properties of TiS2: a never ended story tackled by hybrid functional and many body methods, Inorg. Chem. 2019 (5) Stoliaroff, A.; Latouche, C. ; Jobic, S. 2019

AA.2.4
11:45
Authors : Eric Toberer
Affiliations : Physics Dept., Colorado School of Mines

Resume : This talk will highlight both some of the successes and the stumbling blocks along the way to bring material science into the 21st century. Namely, the combination of (i) high-throughput experiment, (ii) massive computational resources, (iii) machine learning, and (iv) high energy beamline-based studies is more than summative. Given finite human resources (ie graduate students), these tools serve as force multipliers to enhance their capabilities. Over the last decade, we have applied these techniques in concert to the field of thermoelectric materials. This high-throughput search of known and hypothetical compounds has led to the discovery of new classes of materials for these two applications. Most notably, the search reveals entire classes of materials that had been ignored due to historical bias within the thermoelectric community. Through the interplay of materials physics and machine learning, general principles for designing the next generation materials have emerged. The talk will conclude with discussion of the prospects for sequential learning coupled with parallelization and automation to accelerate functional materials discovery.

AA.2.5
12:15
Authors : Stephan Lany
Affiliations : National Renewable Energy Laboratory

Resume : Materials discovery is increasingly going beyond the prediction of thermodynamically stable materials at Daltonian compositions and their crystallographic primitive cells, including, e.g., metastable compounds, solid solutions, as well as defect- and disorder-enabled materials. Due to their relative instability against N2, nitrides are often grown as thin films via non-equilibrium deposition at relatively low temperatures, leading to atomic disorder. Following a broad search for ternary nitrides spaces, we identified novel wurtzite and rock-salt nitrides by first principles crystal structure prediction, including Zn-M (M = Sb, Mo, W) and Mg-M (M = Nb, Ti, Zr, Hf) [1, 2]. The effects of disorder on structure selection and electronic structure properties are studied by Monte-Carlo sampling. Disorder is also the inherent driving force for the formation of solid solutions. We recently studied the formation and the phase diagram of heterostructural alloys, i.e., the mixture of compounds with different crystal structures, such as MnO-ZnO and SnS-CaS [3]. We showed that, compared to the more conventional case of isostructural alloys (e.g. InGaN), heterostructural alloys can exhibit a markedly increased range of metastable compositions between the binodal and spinodal lines, thereby enabling the design of novel homogeneous single-phase alloys. [1] E. Arca et al, J. Am. Chem. Soc. 140, 4293 (2018) [2] W. Sun et al, arxiv/1809.09202 (2018) [3] Holder et al, Sci. Adv. 3, e1700270 (2018)

AA.2.6
12:30 Lunch    
 
Quantum materials and Polymers : -
14:00
Authors : Daniele Torelli, Kristian S. Thygesen, Thomas Olsen
Affiliations : Technical University of Denmark

Resume : The recent observation of ferromagnetic order in two-dimensional (2D) materials highlights the importance of understanding the fundamental aspects of magnetism in 2D materials. In contrast to bulk materials in three dimensions, magnetic anisotropy plays a crucial role for magnetic order in 2D and is therefore intimately linked to spin-orbit coupling. In the present work we have used the Computational 2D Materials Database (C2DB) to search for new ferromagnetic 2D materials. In addition to the well-known ferromagnetic 2D materials CrI$_3$ and VSe$_2$, we find 12 novel insulating materials that exhibit magnetic order and evaluate their critical temperatures from Monte Carlo simulations using our calculated values for exchange and anisotropy parameters. A few of these exhibit critical temperatures exceeding 100 K and could comprise promising candidates for future investigations of magnetism in 2D. We also investigate the effect of Hubbard correction in the frame work of DFT+U and find that the chosen value of U can have a crucial influence on the magnetic properties.

AA.3.1
14:30
Authors : Simon M.-M. Dubois, Bruno Dlubak, Jean-Christophe Charlier, Pierre Seneor
Affiliations : Unité mixte de Physique CNRS/Thales & Institute of Condensed Matter and Nanosciences ,UCLouvain; Unité mixte de Physique CNRS/Thales; Institute of Condensed Matter and Nanosciences, UCLouvain; Unité mixte de Physique CNRS/Thales

Resume : Two-dimensional materials are promising candidates for use as tunnel barrier in atomically thin magnetic tunnel junctions (MTJs) [1]. High magneto resistance ratios have been predicted theoretically and recent progress in large scale manufacturing of these materials has paved the way towards their integrations in functional devices. Yet, the experimental results available so far vary greatly depending on the integration pathways. Seeking for increased performances, it has been shown lately that direct CVD growth of tunnel barriers improves significantly the quality of the ferromagnet-2D materials interfaces [2-4]. Following these recent developments, new phenomena such as the bias induced reversal of the magneto resistance were reported [5]. Here, we show that first-principles calculations can provide direct insights into the close relation that links the interface morphology to its magneto resistive behavior. In particular, we report on the interaction between ferromagnet electrodes and graphene/h-BN 2D layers as well as on the origin of TMR reversal in h-BN based MTJs [5]. References [1] M. Piquemal-Banci et al., J. Phys.D. Appl. Phys., 50 (2017), 203002 [2] S. Caneva et al., Nano Lett.,16 (2016), 1250. [3] M.-B. Martin et al., Appl. Phys. Lett., 107 (2015), 012408. [4] S. Caneva et al., ACS Appl. Mater. Interfaces, 9 (2017), 29973. [5] M. Piquemal-Banci et al., ACS Nano, 12 (2018), 4712.

AA.3.2
14:45
Authors : Taras Radchenko, Valentyn Tatarenko; Ihor Sahalianov, Yuriy Prylutskyy
Affiliations : G.V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine; Taras Shevchenko National University of Kyiv, Ukraine

Resume : We use numerical calculations to study effects of structural imperfections (point and line defects) and external mechanical or magnetic field on electronic and transport properties of graphene sheet comprising millions of atoms, i.e. layer of several hundred nanometres in size. Point defects are modelled as resonant (neutral) adsorbed atoms or molecules, vacancies, charged impurities, and local distortions. Line defects are attributed to atomic steps and terraces in epitaxial graphene, and grain boundaries, nanoripples or wrinkles in polycrystalline graphene. Results are obtained numerically using the quantum-mechanical Kubo-Greenwood formalism and tight-binding approach. Calculated behaviours of electronic density of states and conductivity indicate that deviations from perfection can be useful: they make possible tailoring graphene electrotransport properties for achievement of new functionalities. Particularly, the ordering of point defects can open a band gap in the energy spectrum of graphene, enhance its conductivity up to dozens (10-30) of times; and orientation correlation of linear defects can increase the conductivity up to 4-5 times. If there are both types defects, their ordering and correlation may improve the conductivity up to hundreds of times as compared with their random distribution. The presence of both point and extended defects reduces Landau levels, broadens, smears, and can even suppress them. The utilizing of the combination of the shear strain and uniaxial tensile strain is found to be the easy and stable way for the band-gap opening and tuning.

AA.3.3
15:00
Authors : Yuting Liu
Affiliations : Fernando Bresme; Rongjun Chen; John Seddon

Resume : Synthetic polymers have been widely experimented in its applications for endocytosis drug delivery. To advance the molecular understanding of polymer interaction with charged lipid bilayers, Molecular Dynamics (MD) simulations have been performed using poly (L-lysine iso-phthalamide) grafted with L-phenylalanine in 75 mol% substitution degree (PP-75) and charged binary lipid membranes (DOPC/DOPS). The impact of chain lengths, degree of protonation and monomer sequence have been investigated systematically using MD. Area per lipid and thickness of the bilayer was calculated to determine the membrane geometry change after penetration. These results are helpful to interpret AFM experiments of the polymer adsorbed at biological membranes. Comparison of results with charged and uncharged membranes should provide an understanding of the role of lipid charge on polymer adsorption and penetration in the biological membranes.

AA.3.5
15:15
Authors : Sung Hyun Kwon, Haisu Kang, Ji Hye Lee, Sunbo Shim, Jinhee Lee, Dong Sun Lee, Chi Myung Kim, Seung Geol Lee
Affiliations : Department of Organic Material Science and Engineering, Pusan National University; Department of Organic Material Science and Engineering, Pusan National University; Department of Organic Material Science and Engineering, Pusan National University; Hyundai Motor Company; Hyundai Motor Company; Hyundai Motor Company; Hyundai Motor Company; Department of Organic Material Science and Engineering, Pusan National University

Resume : The performance of polymer electrolyte membrane fuel cells (PEMFCs) is highly dependent on perfluorosulfonic acid (PFSA) polymer electrolyte membranes. In this investigation, we used full atomistic molecular dynamics (MD) simulations to reveal the effect of side chain pendants in PFSA polymers. Through these MD simulations, the structural and transport properties of PFSA polymers are analyzed with different contents of water at room temperature (298.15K) and operating temperature (353.15K) of PEMFCs. We performed the pair correlation function (PCF) analysis and free volume analysis to check morphologies of water inter-connections in PFSA polymer electrolyte membranes which is crucial to generate the water channel for proton conduct and oxygen transport. We also checked the diffusion of water, hydronium and oxygen by mean square displacement (MSD) analysis with different side chain pendants in PFSA polymers at various water contents. Thus, our primary objective in this simulation study is to elucidate the role of side chain pendants in determining the structural and transport properties in PFSA polymers electrolyte membranes, which will shed light on the design of PFSA polymers at a molecular level. Acknowledgement This work was supported by the R&D Collaboration Programs of Hyundai Motor Company.

AA.3.6
15:30
Authors : Pascal Friederich (1), Franz Symalla (2), Artem Fediai(1),Velimir Meded(1), Alexander Colsmann(3),Mario Ruben(1), Wolfgang Wenzel(1)
Affiliations : (1)Institute of Nanotechnology, Karlsruhe Institute of Technology, Germany. (2) Nanomatch GmbH; Karlsruhe, Germany (3)Light Technology Institute, Karlsruhe Institute of Technology, Germany.

Resume : Small-molecule organic semiconductors are used in a wide spectrum of applications, ranging from organic light emitting diodes1 to organic photovoltaics. A number of factors determine mobility, such as molecular packing, electronic structure, dipole moment and polarizability. Presently, quantitative ab-initio models to assess the influence of these molecule-dependent properties, including the influence of dopants, are lacking. Here, we present a multi-scale model, which provides an accurate prediction of experimental data over ten orders of magnitude in mobility,2 and allows for the decomposition of the carrier mobility into molecule-specific quantities. The model consists of a multi-step procedure, incorporating single molecule parameterization, generation of atomistic morphologies,3 DFT based electronic structure calculations yielding site energies, energy disorder, electronic couplings and reorganization energies.4 These parameters are used in an analytic model5 to compute the charge carrier mobility of the amorphous materials. We also provide molecule-specific quantitative measures how two single molecule properties, the dependence of the orbital energy on conformation and the dipole induced polarization determine mobility for hole-transport materials. On the basis of this methodology we are able to computationally predict novel pure ETL materials with three orders of magnitude higher mobility than their precursors and elucidate the molecular mechanism of doping these materials with kinetic Monte-Carlo simulations. The availability of first-principles based models to compute key performance characteristics of organic semiconductors may enable in-silico screening of numerous chemical compounds for the development of highly efficient opto-electronic devices. 1 Groves, C. Organic light-emitting diodes: Bright design. Nat. Mater. 12, 597-598 (2013). 2 Friederich, P. et al. Molecular origin of the charge carrier mobility in small molecule organic semiconductors. Accepted in Adv. Functional Mater.31, 5757, (2016). 3 Neumann, T., Danilov, D., Lennartz, C. & Wenzel, W. Modeling disordered morphologies in organic semiconductors. J. Comput. Chem. 34, 2716-2725, doi:10.1002/jcc.23445 (2013). 4 Friederich, P., Symalla, F., Meded, V., Neumann, T. & Wenzel, W. Ab Initio Treatment of Disorder Effects in Amorphous Organic Materials: Toward Parameter Free Materials Simulation. J. Chem. Theory Comput. 10, 3720-3725, doi:10.1021/ct500418f (2014). 5 Rodin, V. et al. A generalized effective medium model for the carrier mobility in amorphous organic semiconducturs. Phys. Rev. B 91, doi:10.1103/PhysRevB.91.155203 (2015).

AA.3.7
15:45
Authors : Micaela Matta, Richard J. Gowers, Craig T. Chapman, George C. Schatz
Affiliations : Department of Chemistry, Northwestern University, Evanston, IL (United States) and Department of Chemistry, University of Liverpool, Liverpool (United Kingdom); Department of Chemistry, University of New Hampshire, Durham, NH (United States); Department of Chemistry, University of New Hampshire, Durham, NH (United States); Department of Chemistry, Northwestern University, Evanston, IL (United States)

Resume : Molecular π-conjugated semiconductors are used as active materials enabling charge transport for a range of applications in organic electronics. However, the lack of long-range order and elusiveness of structure-property rules hinders the systematic improvement of device performances for these amorphous systems. Molecular dynamics (MD) simulations, combined with the estimation of electronic couplings between molecular neighbors, are often used to study charge transport pathways and their dimensionality. Recent efforts have sought to adapt concepts and algorithms from graph theory and classical resistor theory to define molecular networks made of “electronically connected” units within a bulk amorphous molecular solid. In this representation, every molecule is a node of the graph and electronic couplings are the edges connecting the nodes. We present here an open-source molecular network code that implements and expands these concepts, offers powerful visualization tools and shows a >100x speedup compared to previously published benchmarks. The dynamical properties of the charge percolation networks, such as their lifetime and robustness, can eventually be used to build a macroscopic transport model (ie Kinetic Monte Carlo) including dynamic disorder, similarly to what is being done for crystalline systems. As a case study, we consider the impact of alkyl side chain length on the electronic connectivity, film morphology and photovoltaic efficiency of a series of ITIC derivatives.

AA.3.8
16:00
Authors : Ranjini Sarkar, T. K. Kundu
Affiliations : Indian Institute of Technology Kharagpur; Indian Institute of Technology Kharagpur

Resume : Electro-active polymer β-polyvinylidene fluoride (β-PVDF) based ferroelectric composites have gained significant technological importance over conventional ceramic ferroelectrics. But synthesis of β-PVDF has been a challenge owing to its structural instability. Hydrated metal salt systems are found as one of the additive materials which effectively induce polar β-PVDF from non-polar PVDF blend (which contains majorly α phase). This article provides quantum chemical description of PVDF – hydrated aluminium nitrate salt composite system in the light of density functional theory. Four monomer units of pristine α and β-PVDF, pure Al(NO3)3.9H2O, and PVDF/ Al(NO3)3.9H2O structures are optimized using dispersion corrected exchange correlation functional B3LYP-D3 and 6-311 G(d,p) basis set. Similar to the experimental findings, the current theoretical investigation also suggests that hydrogen bond interaction between PVDF and the hydrated salt molecule plays the major role for the enhancement of ferroelectric properties in this composite system. Non-covalent interaction phenomenon is elucidated in detail on the basis of natural bond orbital analysis, Bader’s quantum theory of atoms in molecules and reduced density gradient analysis. Chemical reactivity and charge transfer mechanisms are explained using molecular electrostatic potential plot, frontier molecular orbital analysis and atomic-dipole corrected Hirshfeld population analysis, respectively.

AA.3.9
16:15
Authors : Ji Hye Lee, Gisu Doo, Sung Hyun Kwon, Sungyu Choi, Hee-Tak Kim, Seung Geol Lee
Affiliations : Department of Organic Material Science and Engineering, Pusan National University; Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST); Department of Organic Material Science and Engineering, Pusan National University; Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST); Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST); Department of Organic Material Science and Engineering, Pusan National University

Resume : Polymer electrolyte membrane fuel cells (PEMFCs) are expected to be useful as energy convertors for transportation and stationary applications, due to its high energy efficiency, low emissions and low working temperature. However, its high production cost and poor long-term durability impede the widespread commercialization process. A significant portion of the total cost is the cost of the membrane electrolyte assembly (MEA). The performance of the cathode catalyst layer in the MEA is a major controlling factor of the ultimate cell performance. Therefore, numerous studies on the understanding of the morphology and characteristics on catalyst layer have been carried out. However, the morphology and accompanying properties about the distribution of ionomer and dispersion solvent on the catalyst layer still involve many unknown aspects. In the present study, a molecular-level morphological insight is gained by means of molecular dynamics (MD) simulation. For controlling the distribution of Nafion ionomer and dispersion solvent on catalyst layer, we alter two key factors: (i) the type of dispersion solvent (dipropylene glycol (DPG), water and DPG/water mixture) and (ii) catalyst surface properties (Pt surface and alkylthiol-modified Pt surface). Depending on the type of dispersion solvent, the dispersion state of Nafion ionomer was changed. As increasing the ratio of dipropylene glycol (DPG) in dispersion solvent, the Nafion ionomer was well distributed in the dispersion solvent. Moreover, we find that the alteration of interfacial components in contact with the surface of catalyst layer take place by changing the surface property of catalyst. These findings can provide new insights into designing the optimized interface structure of catalyst layer, with excellent performance of PEMFC. Acknowledgements This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (Nos. NRF-2015M1A2A2057129 and NRF-2016M1A2A2937151).

AA.3.10
16:30 Coffee break    
 
Poster session : -
17:00
Authors : Akash Oraon, Rajneesh Oraon, Sudipto Ghosh, Shampa Aich, Gautam Sinha
Affiliations : Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, India; Cognizant Technology Solutions, Noida 201304, India; Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, India; Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, India; Raja Ramanna Centre for Advanced Technology, Indore 452013, India.

Resume : The current work presents a methodology of simulation based design of Magnetic Resonance Imaging (MRI) magnets, modified with a symmetric ferromagnetic shell (pure Fe). This design employs the gradient-based optimization solver of COMSOL Multiphysics to obtain an optimum geometrical arrangement of symmetrical electromagnets in MRI. The aim of this work is, to design an MRI magnet system with minimum ampere-turns, high field homogeneity and having magnetic coils with shorter radii. The optimized design solution provides the dimensions of coil blocks, the total length of conductor in each coil block, positions of the coil blocks, current and the resultant magnetic field. The present work reveals that the modification of an MRI system with a ferromagnetic shell significantly improves the field uniformity within a central spherical zone having a diameter of 40-50 cm and greatly reduces the current requirement. The technique used for the optimization can be extended to other kinds of geometries.

AA.P.1
17:00
Authors : Anchalee Junkaew1, Tinnakorn Saelee2, Supawadee Namuangruk1, Nawee Kungwan2
Affiliations : 1 National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency, Pathumthani, 12120, Thailand. 2 Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand

Resume : Propane dehydrogenation (PDH) has been used for producing propylene, which is a crucial precursor for synthesizing a variety of industrial products. Besides the well-known Pt-based catalysts, other catalysts with high reactivity, high selectivity and lower cost have been sought for this application. Among metal-based catalysts, Ni was reported as an active catalyst for hydrogenation and dehydrogenation reactions of small alkanes. However, poor selectivity of propylene production and fast deactivation of Ni were observed in experiment. In this work, a plane-wave based density functional theory (DFT) method had been used to investigate PDH reaction mechanism on bare Ni surface and to study a role of dopant on its catalytic efficiency. Our calculated results revealed that the 1-propyl intermediate is the preferable pathway on bare Ni (111). Our finding also suggested that the strong propylene adsorption on Ni results in poor selectivity and leads to further deep hydrogenation or C-C bond cracking. The calculations clarified the effect of Au or Sn on reactivity of Ni, its selectivity towards propylene production and coke deposition on the surface. Electronic charge properties were elucidated to explain the nature of active sites of those catalysts. This study provides a good guidance for developing Ni-based catalysts used in dehydrogenation of light alkanes.

AA.P.2
17:00
Authors : Marcin Roland Zemła, Tomasz Wejrzawnoski
Affiliations : Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland

Resume : Numerous of applications require water wettability of material surface to be precisely controlled. Superhydrophobic surfaces, defined by the water contact angle being over 150 degree, have received rapidly increasing research interest due to their potential application mostly in areas such as self-cleaning and anti-icing. Following our previous studies regarding cerium, neodymium and europium doped Al2O3, in this work we applied spin-polarized density functional theory (DFT) method to analyse the possibility of tuning the wettability of aluminium surface by graphene coating. The computational model which includes long-range van der Waals interactions were used in order to get proper calculations of graphene geometries and properties. The calculations were performed in order to analyse the interaction between graphene layer, Al(111) surface, and ice-Ih bilayer. Moreover, the obtained results were used to characterise influence of substratum as well as functionalization (fluorination) of graphene to the atomic contact angle. Acknowledgements This work was supported by the European Commission under Horizon 2020 Programme and CARIC/NSERC from Canada in the framework of project PHOBIC2ICE (Grant No. 690819). Computing resources were provided by High Performance Computing facilities of the Interdisciplinary Centre for Mathematical and Computational Modeling (ICM) of the University of Warsaw under Grant No. G64-8.

AA.P.3
17:00
Authors : J. L. Rosas1, J. M. Cervantes2, J. A. León-Flores1, M. Romero3, E. Carvajal2, R. Escamilla1
Affiliations : 1 Universidad Nacional Autónoma de México, Instituto de Investigaciones en Materiales, A.P. 70-360, Ciudad de México, 04510, México; 2 Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica-Culhuacán, Av. Santa Ana 1000, Ciudad de México, 04440, México; 3 Universidad Nacional Autónoma de México, Facultad de Ciencias, A.P. 70-399, Ciudad de México, 04510, México;

Resume : Sr2FeNbO6 is a double perovskite compound which exhibits antiferromagnetic and semiconductor behaviors, an energy gap of ~2 eV and Néel temperature of ~35 K; that make it optimum to be used as SOFCs’ electrode or photocatalyst for H2 generation [1, 2]. However, there are very few research about this compound, possibly due to the high cost associated with their synthesis process. Nevertheless, recently we obtained the SFNO compound by using the molten salts method, in a six hours process, at 900°C, diminishing drastically the associated synthesis cost. The experimental details has been accepted for publication but, in this work, we report supplementary results on the structural and electronic properties of the SFNO compound, under high pressure, studied in the framework of the of density functional theory. Acknowledgments: This work was partially supported by the projects PAPIIT IN109718 and IPN-SIP-2019-6659. Calculations were done using resources the Supercomputing Center DGTIC-UNAM. J. L. Rosas, J. M. Cervantes and J. A. León F. want to acknowledge the scholarship from CONACYT. References: [1] E. D. Jeong, S.M. Yu, J.Y. Yoon, et al., J. Ceram. Process. Res. 3, 305 (2012). [2] K. K. Pandey, et al., AIP Conf. Proc. 1730, 030029-1 (2015).

AA.P.4
17:00
Authors : Eliezer F. Oliveira, Leonardo D. Machado, Douglas S. Galvão
Affiliations : State University of Campinas (UNICAMP), Campinas-SP, Brazil; Federal University of Rio Grande do Norte (UFRN), Natal-RN, Brazil.

Resume : 3D carbon allotropes formed by a carbon nanotubes network can present interesting mechanical and electronic properties. It has been previously shown in the literature that it is possible to grow carbon nanostructures inside the channels of the zeolites. As there is a large number of zeolites, a candidate structure to support the synthesis of 3D carbon nanotubes network could be the beta zeolite, that has its channels interconnected and with same diameter (~5.6Å). Then, we study theoretically from molecular dynamics simulation, the possibility of the existence of one (or more) 3D nanostructures of carbon nanotubes formed inside beta zeolite template, and its resulting mechanical properties. We verified that the carbon nanotube (6,0) can be embedded inside the channel of the beta zeolites keeping the system with the lowest possible energy. From this carbon nanotube, it is possible to built 3D structures with high density (all zeolite channels filled) and lower densities (zeolite channels partially filled). The mechanical properties of the resulting 3D carbon nanotube network with low density indicates mechanical anisotropy and enormous elasticity in the x direction when stretched, supporting more than 100% of strain without fracture. These results suggest that the 3D carbon nanotube network synthesized inside the beta zeolite can be an interesting structure for technological applications.

AA.P.5
17:00
Authors : Kurelchuk Uliana N., Borisyuk Petr V., Vasiliev Oleg S.
Affiliations : National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) 115409, Russian Federation, Moscow, Kashirskoe shosse, 31.

Resume : Ab initio study of thermoelectric properties of model materials made from the d-metallic nanoclusters is presented. Semiclassical thermoelectric transport coefficients had been obtained from the DFT-calculated band structure. Upto 50 times increasing of the Seebeck coefficient was obtained numerically for nanoclustered materials with respect to the bulk one. It stays in agreement with the experimentally observed trends of nanoclusters properties. Relationship of structural, electronic and thermoelectric properties of nanoclusters and structures formed from it, is discussed in order to developing of highly efficient thermoelectric materials.

AA.P.6
17:00
Authors : Miłosz Martynow [1], Damian Głowienka [1], Jędrzej Szmytkowski [1], Yulia Galagan [2], Julien Guthmuller [1].
Affiliations : [1] Faculty of Applied Physics and Mathematics, Gdańsk University of Technology. Narutowicza 11/12, 80-233 Gdańsk, Poland; [2] TNO/Solliance. High Tech Campus 21, Eindhoven 5656AE, Netherlands

Resume : The growth of the human population and the related increase of energy consumption force humanity to find new sources of energies. One of the most promising approach consists of using renewable solar energy sources, e.g. based on photovoltaic panels, which can supplement the limited fossil resources (coal, oil and gas). A semiconductor layer is the heart of every solar panel, which exhibits the photovoltaic effects responsible for the conversion of solar light energy into electricity. One of the newest and most promising photovoltaic solar cells (PVSCs) are based on the perovskite CH3NH3PbI3 material, which have reached high efficiencies of 23% [1, 2]. The main reasons of high conversion efficiency in the perovskite cells are a large absorption coefficient [3], high charge carrier mobility [4], a long electron–hole diffusion length [5] and a direct band-gap of about 1.5 eV being close to the optimal band-gap [6]. Furthermore, perovskite materials have numerous advantages from the social and economical point of views, like low cost of preparation, flexibility, small weight and high transparency [7]. All these points make perovskite PVSCs one of the most promising materials for photovoltaics. However, despite a large amount of investigations on this class of materials, an in-depth understanding of the physical mechanisms lying at the basis of the PVSCs high performance is still to be achieved. In particular, the impact of the orientational disorder of the methylammonium (MA) molecules on the electronic and optical properties still requires clarification. In this poster, we use theoretical calculations coupled with experimental methods to obtain precise information about structural, electronic and optical properties of the CH3NH3PbI3 material. For this purpose, Density Functional Theory (DFT) and Time Dependent DFT (TD-DFT) methods were used to study the perovskite material. A thorough numerical investigation of the possible orientations of the MA molecules within the crystal provided the most stable structures. Then, electronic structure calculations at the TD-DFT level of theory applied to chosen relaxed structures allowed the simulation of the absorption spectrum, which was compared to experimental data.

AA.P.7
17:00
Authors : Simon Kaiser, Franz Symalla, Pascal Friederich, Tobias Neumann, Timo Strunk, Wolfgang Wenzel
Affiliations : Karlsruhe Institute of Technology (KIT), Germany; Nanomatch GmbH, Germany; Karlsruhe Institute of Technology (KIT), Germany & University of Toronto, Canada; Nanomatch GmbH, Germany; Nanomatch GmbH, Germany; Karlsruhe Institute of Technology (KIT), Germany

Resume : Organic light emitting diodes (OLEDs) have seen great improvements since the first prototype in 1987 by Tang and Van Slyke. Today they are widely used in consumer electronics such as smartphones, TVs and general lighting applications. OLEDs in these applications are based on thin films of amorphous organic semiconductors consisting of small organic molecules or polymers exhibiting hopping transport due to the localized nature of the charge carriers. Electrons and holes recombine in emissive layers embedded within multiple charge transport layers. Charge carrier mobility in individual layers can vary by orders of magnitudes depending on the materials, their composition and processing. The main challenge of device optimization is balancing the intricate interdependencies between the individual layers requiring great experimental effort. Here we developed an ab initio multiscale workflow to determine the structure property relations for OLED devices and apply it to single-carrier devices commonly used as charge transport layers. This method, extended to include emissive and injection layers, will allow inexpensive virtual prototyping of OLED devices, complimenting established experimental techniques.

AA.P.8
17:00
Authors : Gabriele Saleh, Sergey Artyukhin
Affiliations : Istituto Italiano di Tecnologia, Via Morego 30, Genova, Italy

Resume : A number of Metal Chalcogenides are promising candidates for cutting-edge applications[1]. IrTe2 displays peculiar T-induced phase transitions[2] that can be tuned by doping and triggered by photoexcitation[3]. These transitions display hysteresis and they are accompanied by a change in the physical properties of the material, thus making IrTe2 attractive for technological applications. The various phases differ by the length of certain Ir-Ir and Te-Te bonds, that change up to 30% [4]. While a wealth of experimental results exist, the atomic-level understanding of IrTe2 behaviour is still poor. In this contribution, we present an in-depth computational investigation of the electronic structure and lattice dynamics of IrTe2. We demonstrate -through the combined use of several chemical bonding analysis approaches- that the electronic stability of low-T phases is determined by the formation of Ir2Te2 4-centre bonds. The high-T phases, instead, is stabilized by the higher entropic contribution of its phonons. We rationalize the observed hysteresis by analyzing the energetics of phase transitions trough the Nudged Elastic Bands method. Finally, we present our preliminary results on the effect of doping on both the band structures and the phonon spectra of the IrTe2 phases. [1] C. Tan et al. , Adv. Mater., 29, 1701392 (2017). [2] Q. Li et al. , Nat. Comm., 5, 5358 (2014). [3] S. I. Ideta et al., Sci. Adv., 4, eaar3867 (2018). [4] J. Dai et al., Phys. Rev. B, 90, 235121 (2014)

AA.P.9
17:00
Authors : Z. Skanderi1* A. Djebaili1 Ilhem. R. Kriba2 Y. Ahmane3
Affiliations : 1 Laboratory of chemistry and environmental chemistry L.C.C.E - University of Batna- Algeria 2 Faculty of Material Sciences- Department of Chemistry - University of Batna 1- 05000- Algeria 3 Faculty of Sciences- Department of Chemistry - University of Biskra- Algeria

Resume : With the aim of finding an interpretation for the isomerization reaction of icosadeca-ene by quantum methods, we have studied a series of three molecules giving the following results:  The studied segments (C20H22, C20H11F11, C20H11Cl11, C20H11Br11 and C20H11I11) are very stable. This stability is justified by the HOMO-LUMO found energy gap. However, examination of the stability of several conformations shows that the trans conformer is more stable than the cis conformer in the general assembly.  According to the study of different reaction profiles, we noticed that the size and nature of the dopant plays a very important role on the evolution of the activation energy.  From the obtained values of the activation energy, we find that the speed constants of the isomerization reaction are in the order: kC20H22 >> k C20H11F11 >> k C20H11Cl11 >> k C20H11Br11 >> k C20H11I11  The search for intermediate products during the transition Cis-Trans shows that the geometric parameters (angles and dihedral angles) are the most varied settings, this remark has been observed in the case of substituted and non-substituted icosadeca-ene.  The methods of calculations performed in this work are the Ab-initio and DFT methods, with the bases (6-31G, 3-21G **). All these calculations are performed with the Hyperchem software, where parameters obtained are in a closer order to those obtained with the Gaussian 03W software  Examination of different molecules obtained during the Cis-Trans isomerization reaction shows that the total energy of the resulting intermediate product is of the order of -10487.05 eV, corresponding to a 0.87eV activation energy (23.67 kcal / mol).  With the same HF method (6-31G and 3-21 G**), a close geometry was obtained for the intermediate product in the isomerization reaction with a total energy of 0.93 eV (25.30 kcal/mole), which shows that the different values of the activation energy obtained by the HF and DFT methods at the 6-31G level can be compared to those obtained by Ito, Montaner and Bernier. Keywords: Ab-initio; DFT; kinetics; isomerisation; substituted icosadeca-ene

AA.P.10
17:00
Authors : D. Bocharov(a), M. Krack(b), Yu. Rafalskij(a), A. Kalinko(c), A. Kuzmin(a), J. Purans(a), S. E. Ali(d), F. Rocca(e)
Affiliations : (a) Institute of Solid State Physics, University of Latvia, Kengaraga street 8, LV-1063 Riga, Latvia (b) Paul Scherrer Institute, CH-5232 Villigen, Switzerland (c) Department Chemie, Naturwissenschaftliche Fakultät, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany (d) Physics Department, Faculty of Science Suez Canal University, Ismailia, Egypt (e) IFN-CNR, Institute for Photonics and Nanotechnologies, Unit FBK-Photonics of Trento, Via alla Cascata 56/C, I-38123 Povo (TN), Italy

Resume : Negative thermal expansion (NTE) is an interesting property of some materials leading to their lattice contraction upon heating. Recently metal fluorides like scandium fluorine (ScF3) have attracted attention as new class of NTE materials. In the present study the NTE effect in ScF3 was studied in the temperature range from 300 K to 1600 K using ab initio molecular dynamics (AIMD) as implemented in the CP2K code. The simulations were performed in the isothermal-isobaric ensemble for several different supercell sizes (from 2a×2a×2a to 5a×5a×5a) to investigate the stability of AIMD simulation results depending of the supercell size. The information on the temperature dependence of the lattice constant, inter-atomic bond angle distributions and radial distribution functions was obtained. The temperature dependence of the experimental Sc K-edge EXAFS spectra was also simulated based on the multiple-scattering formalism to additionally validate the accuracy of the AIMD method. Our results suggest that AIMD calculations are able to reproduce qualitatively the NTE effect in ScF3 which is attributed to the tilting motion of ScF6 octahedra. Financial support provided by project No. 1.1.1.2/VIAA/l/16/147 (1.1.1.2/16/I/001) under the activity ”Post-doctoral research aid” realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged.

AA.P.11
17:00
Authors : Laura M. Jiménez-Díaz, Alma L. Marcos-Viquez, Luis A. Pérez
Affiliations : Instituto de Física, Universidad Nacional Autónoma de México, Apartado Postal 20-364, C.P. 04510, Ciudad de México, México; Instituto Politécnico Nacional, ESIME Culhuacán, Av. Santa Ana 1000, C.P. 04430, Ciudad de México, México

Resume : A density functional theory (DFT) study of the structural and electronic properties of isolated neutral clusters of the type Au12M, with M = Cu, Ag, or Ir has been performed. Since there is experimental evidence that the gold-iridium [1], gold-copper [2] and gold-silver [3] nanoparticles have an enhanced catalytic activity for the carbon monoxide oxidation reaction, we also performed DFT calculations of the adsorption and dissociation of molecular oxygen on these nanoparticles. Moreover, to understand the effects of Cu, Ag, and Ir impurity atoms on the dissociation of molecular oxygen, we also analyze this reaction in the corresponding pure gold cluster. The results indicate that the substitution of one gold atom in a Au13 cluster by Ag, Cu or Ir diminishes the activation energy barrier for the oxygen molecule dissociation by nearly 1eV. This energy barrier is similar for Au12Ag and Au12Cu, whereas for Au12Ir is even lower [4]. These results suggest that the addition of other transition metal atoms to gold nanoclusters can enhance their catalytic activity towards the CO oxidation reaction, independently of the effect that the substrate could have on supported nanoclusters. This work was supported by UNAM-PAPIIT IN10717. Computations were performed at the supercomputer Miztli of DGTIC-UNAM (Project LANCAD-UNAM-DGTIC-180). A.L.M.V. would like to thank CONACYT and BEIFI-IPN for her scholarship. References [1] A. Gómez-Cortés, G. Díaz, R. Zanella, H. Ramírez, P. Santiago, J.M. Saniger, J. Phys. Chem. C 113, 9710 (2009). [2] A. Sandoval, C. Louis, R. Zanella, Appl. Catal. B 140-141, 363 (2013). [3] A. Sandoval, A. Aguilar, C. Louis, A. Traverse, R. Zanella, J. Catal. 281, 40 (2011). [4] L.M. Jiménez-Díaz, L.A. Pérez, accepted for publication in ‎Eur. Phys. J. D (2018).

AA.P.12
17:00
Authors : Weisen Zheng, Huahai Mao, Yanlin He, Malin Selleby, John Ågren, Xiao-Gang Lu, Jinyan Ning, Yingying Chen
Affiliations : Weisen Zheng, Yanlin He: School of Materials Science and Engineering, Shanghai University, 200444 Shanghai, China; Huahai Mao, Malin Selleby, John Ågren:Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden; Xiao-Gang Lu, Jinyan Ning, Yingying Chen: Materials Genome Institute, Shanghai University, 200444 Shanghai, China

Resume : In the austenitic lightweight steels, the nano-size precipitates within the austenitic matrix significantly contribute to the improvement of the yield strength. In the present work, the yield strength was predicted by computational approach. Thermodynamic, diffusion mobility and volume databases for lightweight steels was constructed by using both computational and experimental techniques, including CALPHAD, ab initio calculations and diffusion-couple method. Based on the present databases, the precipitation of the ?-carbide during aging was simulated to obtain the volume fraction and mean particle radius. Combining with the models for the solid solution strengthening, grain boundary strengthening, coherency strengthening, anti-phase boundary strengthening and modulus strengthening, the yield strength is predicted for the austenitic lightweight steel with finely dispersed nanometre-sized ?-carbide. The quantitative relationship between the alloy composition, aging parameters, precipitation behavior and the yield strength was established for lightweight steels in the present work.

AA.P.13
17:00
Authors : Bartłomiej Dec, Robert Bogdanowicz
Affiliations : The authors gratefully acknowledge financial support from National Centre for Science and Development Grant Techmatstrateg No. 347324 2015/16/T/ST7/00469.

Resume : The first-principle study with the use of density functional theory (DFT) was performed to evaluate the electrical properties of the boron-doped diamond (BDD) sensor. In calculations, general gradient approximation exchange-correlation was used for the description of energy functional. In this work optimized norm-conserving, Vanderbilt pseudopotential basis set was used [1]. All methods were implemented in software QuantumATK 2018.06 from Synopsys [2]. Periodic slab models were created with six carbon layers passivated with hydrogen atoms on (111) surface. Two boron atoms were placed within the second carbon layer from the top surface. The results show that ligand-functionalized BDD electrodes expose lower electron density on the plane passing through the top amino acids of the protein complex. The BDD structure donates electrons to ligand and protein complexes, resulting in cross-sectional tunelling. The corresponding pathways revealed a high probability of intermolecular charge transfers, which has demonstrated high diffusion to the electrode, due to the high in-plane surface charge transfer. Analysis of structure with bias potential in the range from 0.0 to 2.0 V exposed that the current transport is higher as the length of the molecule is shorter. Bias potential applied to the electrode showed that both systems have exhibited a minor increase in the current up to a certain threshold, after which a step increase was seen due to resonant transmission. The benzoic group forms a near perfect resonant transmission couple [3], which results in excellent performance of the biosensing electrode. References 1. Garrity, K. F., Bennett, J. W., Rabe, K. M. & Vanderbilt, D. Computational Materials Science 81, (2014), 446–452. 2. QuantumATK Atomic-Scale Modeling for Semiconductor & Materials, (2018) 3. Stokbro, K., Taylor, J., Brandbyge, M., Mozos, J.-L. & Ordejón, P., Computational Materials Science 27, (2003), 151–160.

AA.P.14
17:00
Authors : J. L. Rosas, J. M. Cervantes, J. A. León-Flores, M. Romero, J. A. Arenas, E. Carvajal, R. Escamilla
Affiliations : Universidad Nacional Autónoma de México - Instituto de Investigaciones en Materiales, Instituto Politécnico Nacional-Escuela Superior de Ingeniería Mecánica y Eléctrica Unidad Culhuacán, Universidad Nacional Autónoma de México-Facultad de Ciencias, Universidad Nacional Autónoma de México, Instituto de Física

Resume : Double perovskite compounds could be used in fuel cells, spintronics or information storage devices or Li-ion batteries. This variety of applications is linked to physical and chemical properties which is possible to change if, in the perovskite type compounds, the transition metal atoms are replaced total or partially, generating specific solid solutions. This is the case for the compounds Sr2FeMo1-xNbxO6, for which it has been reported experimental results: the ferromagnetic and the half-metallic behaviors shown by Sr2FeMoO6 change, when Nb is incorporated instead of Mo, for x≈0.7. There are enough theoretical and experimental information about the electronic, magnetic and structural properties of Sr2FeMoO6; however, theoretical studies for Sr2FeMo1-xNbxO6 are scarce. In this work we present the results from a first principles study, in the framework of the density functional theory, through the exchange-correlation functional CA-PZ within LDA+U as it is implemented in the CASTEP code. The semiconductor and antiferromagnetic behaviors of Sr2FeNbO6 were reproduced, as well as the corresponding half-metallic and ferromagnetic for Sr2FeMoO6, then the solid solution Sr2FeMo1-xNbxO6 is studied by means of a supercell model for x = 0, 0.25, 0.5, 0.75 and 1. Acknowledgments: This work was partially supported by the projects DGAPA-UNAM IN109718, IA106117 and IPN-SIP-2019-6659. J. L. Rosas, J. M. Cervantes and J. A. León and acknowledge the scholarship from CONACYT.

AA.P.15
17:00
Authors : Chirawat Chitpakdee, Anchalee Junkaew, and Supawadee Namuangruk
Affiliations : National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency, 111 Thailand Science Park, Pathum Thani 12120, Thailand

Resume : Reaction mechanism of the selective catalytic reduction of nitric oxide (NO) by ammonia (SCR-NH3 of NO) on the Ru doped CeO2 surface was investigated using density functional theory calculation corrected by on-site Coulomb interactions (DFT+U). The SCR-NH3 of NO mechanisms on Ru-CeO2, consisted of two consecutive reduction pathways, were systematically examined. The calculated results reveals that the Ru dopant affects on the electronic charge property and enhances the Lewis acidity of the CeO2 (111) surface. NH3 adsorption/dissociation and NO reduction via the NHNO intermediate are facile when the Ru site presents on the catalyst surface. The second NO reduction, which occurs over the presence of the Brønsted acid site, is slightly difficult in terms of NH3 adsorption and dissociation. For the overall reactions, the water formation is the rate determining step. Our results revealed that the Ru dopant greatly enhances the efficiency of the SCR-NH3 of NO reaction of the CeO2 catalyst. The performance of this catalyst can be further enhanced by improving the water formation aspect. The obtained results deepen the fundamental understanding the role of the different active sites on the crucial steps during the reaction.

AA.P.16
17:00
Authors : Gustavo Guarise Pereira, Ricardo Paupitz
Affiliations : Sao Paulo State University (UNESP), Brasil

Resume : In the last few decades, many types of new materials have been proposed and sometimes their synthesis was experimentally achieved. Relevant examples are new allotropic forms of carbon like Graphenylene, which was recently synthesized, or other interesting low dimensional materials, such as Porous Graphene. Both are of great technological interest due to their special mechanical and electronic properties. In our investigation, we used Density Functional Theory and Molecular Dynamics methods to investigate the possibility of tuning the mechanical and electronic properties of Porous Graphene and Graphenylene using different configurations of adsorbed molecules on these materials. Our calculations show that mechanical properties such as the Young modulus, Poisson ratio and the bulk modulus can be modified as well as some electronic features, like the band gap openings, the local density of states and electronic transport properties. For this regard, in the calculations presented in this work we considered the effect of small molecules (e.g. CO2 and O2) or individual atoms, as H and F, adsorbed on graphenylene and Porous Graphene membranes as well as the effect of metallic atoms, such as Co and Fe on the electronic and mechanical properties of those two materials.

AA.P.17
17:00
Authors : V. V. Golovanova, N. V. Tkachenko, T. T. Rantala, J.R. Morante, V. V. Golovanov
Affiliations : IREC, Catalonia Institute for Energy Research, Jardins de les Dones de Negre 1, 08930 Sant Adrià de Besòs, Barcelona, Catalonia, Spain; Department of Chemistry and Bioengineering, Tampere University of Technology, P.O. Box 541, FI-33101, Tampere, Finland; Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101, Tampere, Finland; Center for Innovation Technologies, South-Ukrainian National University, Staroportofrankovskaya Str. 26, 65008, Odessa, Ukraine

Resume : Macrocyclic dyes such as phthalocyanine and porphyrin molecules are well-known harvesting compounds for dye-sensitized solar cells (DSSC). A theoretical DFT approach was used to study the effects of orientation of the dyes on (10-10) wurtzite surface as well as the role of adsorbate-induced surface dipoles on the dye-semiconductor electron transfer (ET). Tilting of the dyes has a dual effect on the photoinduced ET. Shortening of the distance between moieties enhances the tunneling probability for the electrons due to the stronger coupling between the conduction band minimum and LUMO of the dye. By contrast, strengthening of the electronic interactions upon the tilting may significantly affect the relative position of electronic levels and eventually hinder ET. Furthermore, linker of the molecule provides an intermediate state which may affect the hole transfer from the semiconductor to the dye. The peripheral substituents both reduce aggregation effects and shift the energy position of dye’s frontier orbitals that provides alternative ways for excited state relaxation. In addition, various adsorbates on wurtzite surface induce dipole moments, which may facilitate or hinder the ET. By combining spectroscopy studies with DFT methods we deduce that motion of the dye linked to the surface can be in control of the ET at few tens of ps or longer time. We conclude that proper choice of quantum dot ligands and the peripheral substituents can facilitate the photoinduced ET in DSSC.

AA.P.18
17:00
Authors : B. Santic
Affiliations : R. Boskovic Insitute, Zagreb, Croatia

Resume : Quantum wells (QW), quantum steps (QS), and quantum dots are usually assumed to have a rectangular potential profiles. We examine the potential profiles of a narrow QW and determine its effective width. We also study the charge transport via molecular dynamics (MD) simulations. We take the single and double dipole layers as electrostatic models for QS and QW. In addition the molecular dynamics (MD) is performed to study transport properties. As a practical example, we study the dipole layers formed by the ions in the GaN semiconductor. We show that the potential profiles are not rectangular. A quantum step is a continuous change of potential over a distance larger than one monolayer. Our approach provides insight into the relation between the potential profile and the positions of the ions in the crystal planes. Remarkably, the minimal thickness of the QS is not determined by the distance between the charged planes, but by the lateral spacing between ions. Due to the smooth potential profiles of the narrow QWs, the energy levels of localized states are shifted in comparison to a rectangular QWs. In the example of GaN, QS cannot be thinner than about 3 Å.

AA.P.19
17:00
Authors : Sergey M. Karabanov (1), Dmitry V. Suvorov (1), Dmitriy Y. Tarabrin (1), Andrey A. Trubitsyn (1), Andrey E. Serebryakov (1), Evgeny V. Slivkin (1), Andrey S. Karabanov (2), Oleg A. Belyakov (2)
Affiliations : 1 - Ryazan State Radio Engineering University; 2 - Helios Resource Ltd.

Resume : Mathematical modeling makes it possible to reduce time and cost for the development of complex technological processes. The paper presents a complex study of the metallurgical-grade silicon purification technology by vacuum refining and plasma-chemical purification under the conditions of electromagnetic stirring of silicon melt by mathematical modeling. The paper presents the numerical models of the processes, using COMSOL Multiphysics software. The initial and boundary conditions of these processes are formed with HSC Chemistry software. To study vacuum refining under the conditions of electromagnetic stirring, mathematical models including Maxwell equations, hydrodynamics equations for incompressible liquid, mass transfer equations, including directional mass transfer and diffusion for the impurity transportation calculation inside silicon melt are used. For mathematical modeling of plasma-chemical silicon purification, HSC Chemistry software is used. For the thermodynamic estimation of the chemical processes, the change of the Gibbs free energy has been calculated. The research has shown the efficiency of using mathematical modeling for the study of complex technological processes, especially, the technology for purification of metallurgical-grade silicon to solar-grade silicon level using vacuum refining and plasma-chemical purification of silicon melt under the conditions of electromagnetic stirring.

AA.P.20
17:00
Authors : Sergey M. Karabanov (1), Dmitry V. Suvorov (1), Dmitriy Y. Tarabrin (1), Andrey A. Trubitsyn (1), Andrey E. Serebryakov (1), Evgeny V. Slivkin (1), Andrey S. Karabanov (2), Oleg A. Belyakov (2)
Affiliations : 1 - Ryazan State Radio Engineering University; 2 - Helios Resource Ltd.

Resume : Mathematical modeling makes it possible to reduce time and cost for the development of complex technological processes. The paper presents a complex study of the metallurgical-grade silicon purification technology by vacuum refining and plasma-chemical purification under the conditions of electromagnetic stirring of silicon melt by mathematical modeling. The paper presents the numerical models of the processes, using COMSOL Multiphysics software. The initial and boundary conditions of these processes are formed with HSC Chemistry software. To study vacuum refining under the conditions of electromagnetic stirring, mathematical models including Maxwell equations, hydrodynamics equations for incompressible liquid, mass transfer equations, including directional mass transfer and diffusion for the impurity transportation calculation inside silicon melt are used. For mathematical modeling of plasma-chemical silicon purification, HSC Chemistry software is used. For the thermodynamic estimation of the chemical processes, the change of the Gibbs free energy has been calculated. The research has shown the efficiency of using mathematical modeling for the study of complex technological processes, especially, the technology for purification of metallurgical-grade silicon to solar-grade silicon level using vacuum refining and plasma-chemical purification of silicon melt under the conditions of electromagnetic stirring.

AA.P.21
17:00
Authors : Sergey M. Karabanov (1) s, Dmitry V. Suvorov (1), Dmitriy Y. Tarabrin (1), Andrey E. Serebryakov (1), Evgeny V. Slivkin (1), Andrey S. Karabanov (2), Oleg A. Belyakov (2)
Affiliations : Ryazan State Radio Engineering University(1); Helios Resource Ltd. (2)

Resume : Currently, multicrystalline silicon (mc-Si) is the main material for solar cell production. Constant process to the improvement of solar cell specifications requires better crystals quality. Multicrystalline silicon ingots manufactured by directional solidification (DS) contain peripheral areas with contaminations that diffuse during crystallization from the crucible to the ingot. The availability of areas with contamination in silicon wafers results in production of solar cells with lower efficiency. For the registration of these areas, the silicon wafer photoluminescence (PL) method is used, since these areas give a signal with reduced average PL intensity. To control diffusion from the crucible, silicon nitride (Si3N4) protective diffusion coatings are used. The protective coating efficiency depends on its composition, thickness and the layer stability. In the paper, the data science as the most demonstrative and information intensive approach for studying contaminated areas in the ingot volume is used. The method of 3D visualization of recombination active defects with a large number of PL images of mc-Si wafers is applied. The analysis of the effect of using protective coating of different composition and thickness on the area of contaminated zones has been investigated.

AA.P.22
17:00
Authors : Chang-Youn Moon
Affiliations : Korea Research Institute of Standards and Science

Resume : FeSe is unique among other iron-based superconductors, which exhibits no magnetic ordering and becomes superconducting below 8 K in the undoped bulk system while the superconducting transition temperature soars by an order of magnitude for a monolayer FeSe on SrTiO3 substrate. Using a DFT+DMFT framework, we perform a comparative study on the magnetic properties of FeSe systems and LaFeAsO, another representative iron-based superconducting material. Calculated magnetic moment in the typical stripe-type magnetic ordering pattern is finite for LaFeAsO while negligible for bulk FeSe, consistently with experiments, and is also finite for monolayer FeSe suggesting the magnetic order is restored in monolayer FeSe. We suggest a mechanism explaining why the systems with the similar magnitudes of fluctuating spin (S2) have very different magnitude of ordered moment (Sz) focusing on the different aspects of local charge fluctuation. Our work provides a comprehensive understanding of magnetism in iron-based superconducting materials, and also emphasizes on the potential importance of magnetism in the high superconducting transition temperature of monolayer FeSe on SrTiO3 substrate.

AA.P.23
17:00
Authors : Politov B.V., Marshenya S.N., Mychinko M.Yu., Suntsov A.Yu., Shein I.R., Kozhevnikov V.L.
Affiliations : Politov B.V. - Institute of solid state chemistry UB RAS Suntsov A.Yu. - Institute of solid state chemistry UB RAS Shein I.R. - Institute of solid state chemistry UB RAS Kozhevnikov V.L. - Institute of solid state chemistry UB RAS Mychinko M.Yu. - Institute of solid state chemistry UB RAS Marshenya S.N. - Institute of solid state chemistry UB RAS

Resume : Nowadays the great demand for ecologically appreciable ways of creating electricity is observed worldwide. One of the possible solution options is closely linked with creation and commercialization of intermediate temperature solid oxide fuel cells (IT SOFCs) – electrochemical devices capable for efficient energy production without sufficient damage to the environment. The development of the respective materials for various IT SOFC components is a complex, nontrivial task requiring combined theoretical and experimental approach. In particular, design of good SOFC cathode acquires of great importance. Cobaltites containing Ba and Pr are among the best possible candidates, however, their tolerance to carbon dioxide is not high enough. It was already shown that doping with highly charged cations, i.e. Ta5+ or Nb5+, can sufficiently improve cathodes’ working stability limit. This work is aimed at finding out how Nb and Ta doping can influence on PrBaCo2O6–δ oxide’s crystal and electronic structure, defect formation peculiarities and physical properties. The main focus of this study was shifted towards ab initio calculations, however, experimental methods including X-Ray and electron diffraction were also utilized. One of the main findings in this study is the discovery of the different cationic orderings for Nb and Ta doped samples observed experimentally and validated theoretically.

AA.P.24
17:00
Authors : A. Daboussi 1;2, L. Mandhour 1;3 and S. Jaziri 1;4
Affiliations : 1. Université de Tunis El Manar, Faculté des Sciences de Tunis, Laboratoire de Physique de la Matière Condensée, Campus Universitaire Tunis, El Manar, 2092 Tunis, Tunisie. 2. Ecole Supérieure Privée d'ingénierie et de communication, 85-87 Rue Palestine, 1002 Tunis, Tunisie. 3. Université de Tunis El Manar, Institut Supérieur des Technologies Médicales de Tunis, 9 Rue Zouhair Essafi ,1006 Tunis, Tunisie. 4. Université de Carthage, Faculté des Sciences de Bizerte, Laboratoire de Physique des Matériaux, Jarzouna, 7021 Bizerte, Tunisie.

Resume : We show that a stacking defect or a shift has a striking effect on carrier transport of bilayer graphene. Charge transport through a ballistic n–neutral–n junction of shifted bilayer graphene may result in minimal conductivity and shot noise anomalies which are found to be sensitive to the shift defect. Minimum conductivity and shot noise in shifted bilayer graphene exhibit an anisotropic beahavior as a function of the orientation of the electrodes. The minimum conductivity could be suppressed for somme specific value of twist defect while the shot noise takes the unit value. Our results provide a way to control transport properties in an undoped graphene bilayer structure by adjusting the layer stacking.

AA.P.25
17:00
Authors : Aarti Tewari, Santanu Ghosh, and Pankaj Srivastava
Affiliations : Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India

Resume : Surface modification of nanostructures with functional moieties can substantially alter the surface charge, functionality, and reactivity of the surface to extend their usage in practical applications. In the present study, the numerical modeling is employed to examine the field emission properties of graphene-CNT (g-CNT) hybrids via hydrofluoric (HF) acid functionalization. The reaction kinetics of HF acid with acetylene as a precursor gas in an argon plasma medium is considered for the growth of functionalized g-CNT hybrids. The model includes the charging of hybrid surface, the kinetics of the plasma species (neutrals, ions, and electrons), and various processes exclusive to a plasma-exposed surface such as adsorption, thermal dissociation, ion-induced dissociation, and interaction between neutral species among others. The modeling results show that HF acid functionalization remarkably enhances the field enhancement factor of g-CNT hybrids. The enhancement in the electron emission characteristics is attributed to the chemical modification of the carbon network on the hybrid surface. The HF acid acts as an etchant to remove the oxygen atom and replacing the carbon-oxygen (C–O) molecules with carbon-fluorine(C-F) bond. The results of the work can be extended to improve the field emission from g-CNT hybrids. References [1]A. Tewari, S. Ghosh, and P. Srivastava, Phys. Plasmas 25, 043503(2018). [2] A. Tewari, P. Srivastava and S. Ghosh, Phys. Plasmas 25, 083520(2018).

AA.P.26
17:00
Authors : B. Moses Abraham, Vikas D. Ghule, and G. Vaitheeswaran
Affiliations : Advanced Centre of Research in High Energy Materials (ACRHEM), University of Hyderabad, Prof. C. R. Rao Road, Gachibowli, Hyderabad-500046, Telangana, India; Department of Chemistry, National Institute of Technology, Kurukshetra, 136119 Haryana, India; School of Physics, University of Hyderabad, Prof. C. R. Rao Road Gachibowli, Hyderabad 500046, Telangana, India.

Resume : Developing novel energetic materials with high detonation performance and low sensitivity is one of the hottest concerns in the field of explosive research. By employing quantum mechanical tools, a series of energetic ionic salts (EIS) based on 5,5'-bitetrazole-1,1'diolate (BTO) such as ABTOX, DMA-BTO, DU-BTO, HA-BTO, M2-BTO, TKX-50 were thoroughly investigated to obtain more comprehensive insight into structure-property-performance interrelationship. The physicochemical and detonation characteristics of these EIS including structural, electronic, vibrational and performance parameters (heats of formation, detonation pressures, and detonation velocities) were discussed in detail. The D-H stretching vibrations of hydrazine cations are located at much lower frequency followed by hydroxylammonium and their corresponding shorter D...A contacts represent the presence of strong hydrogen bonding environments in the crystal structures of HA-BTO and TKX-50. Careful inspection of various EIS revealed that the hydroxylammonium and hydrazine cations produce the highest density relative to other cations when combined with the BTO anion. The calculated detonation characteristics demonstrate these BTO salts as potential explosives, especially, HA-BTO and TKX-50 provide superior detonation pressure (38.85 and 40.23 GPa) and detonation velocities (9.94 and 9.91 km/s), superior to those of traditional nitrogen-rich energetic materials with moderate sensitivities. Therefore, in this study, we propose that enhancing hydrogen bonding interactions is the main strategy in designing high energy density materials for next-generation explosives, propellants, and pyrotechnics.

AA.P.28
17:00
Authors : K. V. Khishchenko
Affiliations : Joint Institute for High Temperatures RAS, Moscow, Russia

Resume : Models of thermodynamic properties and phase transformations of materials are necessary for simulations of different processes at high energy densities. In this work, an equation-of-state model for metals is presented with taking into account melting and evaporation effects. Equation of state for molybdenum is developed. As distinct from the previously obtained equation of state for the metal [1], a new form of functional expression of thermodynamic potential terms is proposed. These terms provide for more correct thermal contributions of atoms in the solid and liquid phases as well as the phase changes effects. A critical analysis of obtained results is made in comparison with available experimental data at high temperatures and pressures. [1] V. E. Fortov, K. V. Khishchenko, P. R. Levashov and I. V. Lomonosov, Nucl. Instr. Meth. Phys. Res. A 415, 604 (1998).

AA.P.29
17:00
Authors : Jun-Yeong Jo, Ki-Yung Kim, In-Gyu Choi, and Yeong-Cheol Kim
Affiliations : School of Energy Materials and Chemical Engineering, KOREATECH, Cheonan, Republic of Korea

Resume : PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF), a mixed ionic-electronic conductor (MIEC), is a potential cathode of proton-conducting ceramic fuel cells because it shows high surface reaction with oxygen and its diffusivity into bulk [1]. Pr, Ba and Sr go to A site, and Co and Fe to B site in the ABO3 perovskite structure. Pr is known to be separated from Ba and Sr, and they form two different A site layers, A' and A'' respectively [2]. Oxygen vacancies are also known to form in the A' layer and Co adjacent to the oxygen vacancies. We used genetic algorithm (GA) to study energetically favorable distribution of atoms in PBSCF [3]. Separation of Pr from Ba and Sr was first confirmed by GA at a 2x2x2 supercell, and the rule was employed for 4x2x2 and 4x4x2 supercells; this substitution region restriction method reduces the number of configurations for atom distribution, accelerating the GA search further. We will discuss the distribution of Co and Fe atoms in B site. References [1] S. Choi, et al., Sci. Rep., 2013, 3, 2426. [2] A. A. Taskin, et al., Prog. Solid State Chem., 2007, 35, 481. [3] J. Kim, et al., Comput. Mat. Sci., 2017, 138, 219.

AA.P.30
17:00
Authors : Jelena Belić, Prof. Dr. Lucas Visscher
Affiliations : VU Amsterdam, De Boelelaan 1105, 1081 HV Amsterdam

Resume : The production of solar fuels consists of harvesting sunlight as an energy source and transforming it in storable fuel form. One feasible way of doing this is by splitting water. After first example of photoelectrical system , the idea of using dye-sensitized semiconductor electrodes, linked to the water oxidation catalyst was embraced by the community. The interface between electrode and photosensitive component is notoriously complex system as it involves processes of light absorption, charge separation and charge transport. The advantage of this strategy of separating the semiconductor from the photo-sensitive part mimics the process of natural photosynthesis , separating different functions into different parts of the device. Efficiency of these type of cells heavily depends on dye’s characteristics and affinity towards fast electron injection into a semiconductor electrode with low charge recombination. For classes of molecules like naphthalene diimides it is known that properties like HOMO-LUMO energies and their relative gaps are easily tuned by choosing appropriate functional groups . Screening large number of molecules through automated procedure and usage of fast theoretical methods, will provide the molecule with most promising optical and redox properties. These properties are explored with the Amsterdam Density Functional (ADF) code at DFT and DFTB level and also time dependent DFT (TD-DFT and TD-DFTB).

AA.P.31
17:00
Authors : D. Taharchaouche1 Z. Skanderi1* Ilhem. R. Kriba2 Y. Bouzaher1 A. Djebaili3
Affiliations : D. Taharchaouche1, Z. Skanderi1*; Ilhem. R. Kriba2, Y. Bouzaher1, A. Djebaili3 1 Faculty of Sciences- Department of Chemistry - University of Batna 2- Algeria 2 Faculty of Material Sciences- Department of Chemistry - University of Batna 1- 05000- Algeria 3 Laboratory of chemistry and environmental chemistry L.C.C.E - University of Batna 1- Algeria

Resume : DFT calculations, carried out with different basis sets, for the static longitudinal linear polarizability, αL, and second order hyperpolarizability, γL, of small doubly charged hexadecaocta-ene chains, are presented. To demonstrate the stability of several conformations studies of different reaction profiles, determination of rate constants of isomerization reactions and activation energies were made. A theoretical study of a new range based molecules substituted hexadecaocta-ene having the structure D-Π-A by the methods DFT, AM1, PM3 and PM6 finally we can highlight: • The effectiveness of the methods used to calculate the polarizabilities αL, hyperpolarizabilities γL and their components. • The correlations found between the various physical parameters and electronic substituted hexadecaocta-ene and its value exceeds 0.88 average polarizability allowing us and precise quantitative determination of the polarizability for systems with more than 80 atoms by simple extrapolation. • The PM6 method is an effective alternative methods CPHF / TDHF, DFT for the calculation of polarizabilities. The results obtained for positive and negative chains show that the ionization state effect decreases more rapidly, as the chain length is increased, for αL than for γL. Or both types of charged chains, the incorporation of the electron correlation increase the αL, and γL values, as compared to the DFT values. A comparison between the results obtained using the standard 6-31G basis set and augmented versions of this set, obtained by the addition of diffuse and polarization functions, shows that 6-31G basis set does not provide a good description of the negative chains studied here and that the addition of extra diffuse functions on the basis set is needed in order to obtain reliable estimates for polarizabilities, specially for γL. Key words : polarizabilities; hyperpolarisability; hexadecaocta-ene; DFT, AM1, PM3 , PM6

AA.P.32
17:00
Authors : Anastasia Markina1, Frédéric Laquai2, Denis Andrienko1,2
Affiliations : Max Planck Institute for Polymer Research, Mainz, Germany King Abdullah University of Science and Technology (KAUST), KAUST Solar Center (KSC), Physical Sciences and Engineering Division (PSE), Material Science and Engineering Program (MSE), Thuwal 23955-6900, Kingdom of Saudi Arabia

Resume : One promising method to achieve higher solar cell efficiencies is to replace fullerenes with strongly-absorbing dye molecules, namely, nonfullerene acceptors (NFAs). However, the systematic design of acceptor molecules with tailored properties has yet to be demonstrated. The main difficulty here is that, while fullerenes are electrostatically inert, new acceptor molecules typically have strong static quadrupole moments. By exploring the long-range electrostatic interaction at the interface, we demonstrate that, for a set of recently developed NFAs, the electrostatic bias potential can be directly related to the stabilization (or destabilization) of charge-transfer (CT) states as well as changes of the photovoltaic gap. We find that the correlation between quadrupole moments, charge separation efficiency, and CT-state energy predicted by our model, is experimentally reproduced for several different donor /acceptor combinations. This allows us to predict new NFA structures using combinations of readily available molecular building blocks that can potentially reach even higher performances than those currently achieved in stateof-the-art NFA devices.

AA.P.33
17:00
Authors : S. Piskunov, I. Isakovica, A. I. Popov, E.A. Kotomin
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063, Latvia

Resume : Properties of ABO3 perovskite surfaces are strongly dependent not only on their perfectness, but also on reconstruction, defects, as well on the polarity, termination (AO or BO2), and the temperature (because of the both bulk and surface-related phase transitions). In this study the surface phase transitions on SrTiO3 (001) and related surfaces are simulated for the first time at the ab initio level using the state of the art DFT hybrid approach (HSE06 Hamiltonian), with accuracy much higher than in any previous theoretical studies. Raman frequencies for surface defects and their liminescence properties have been calculated. Predicted tiny surface reconstruction due to phase transitions and vibrational defect properties can be checked with RHEED, Raman and CL measurements. Understanding and control of the surface-related properties of advanced SrTiO3 perovskites is important for applications in microelectronics and catalysis. Funding from Latvian-Ukraine biletaral project is greatly acknowledged.

AA.P.34
17:00
Authors : Samar Dabbabi1, Tarek Ben Nasr1, Mejda Ajili1, A. Garcias-Loureiro2, Najoua Kamoun1
Affiliations : 1. Université Tunis El Manar, Faculté des Sciences de Tunis, Département de Physique, LR99ES13 Laboratoire de Physique de la Matière Condensée (LPMC), 2092 Tunis, Tunisia 2. Centro Singular de Investigación en Tecnoloxías de Información (CiTIUS), Universidad de Santiago de Compostela, España

Resume : The new solar cell architecture is relatively complex and requires a thorough understanding of the materials behavior, involving accurate knowledge of the structural, morphological, optical and electrical properties of these materials. In this work, we have used the Silvaco-Atlas software to optimize a specified conception of the FTO/Co-ZnO/CuO hetero-junction structure by taking account of the materials parameters. Firstly, the CuO solar cell and its layer structure were prepared by spray pyrolysis method on glass substrates in order to characterize physical material parameters using Raman spectroscopy, Transmission electron microscopy, Scanning electron microscopy, and Hall Effect measurements. Secondly, theobtained physical parameters were used in simulation. Thickness and carrier concentration effects of the cell structure were studied to optimize the solar cell performances.The combination of the optimum parameters enables us to optimize and to obtain the efficiency of 24.55 % which is improved with 8.88 % compared to the reference one which is the high record conversion efficiency found experimentally in the CuO solar cell[1].

AA.P.35
17:00
Authors : Bernard K. Wittmaack, Alexey N. Volkov, Leonid V. Zhigilei
Affiliations : Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, USA; Department of Mechanical Engineering, University of Alabama, Tuscaloosa, Alabama, USA

Resume : Vertically aligned carbon nanotube (VACNT) arrays or “forests” behave mechanically as foams when compressed, exhibiting a characteristic nonlinear stress e strain response. However, the fiber structure of VACNT forests is unlike that of cellular foams, and the microscopic mechanisms of the deformation are quite different. While numerous studies have addressed the mechanical response of VACNT forests undergoing uniaxial compression, the underlying deformation mechanisms are not yet fully established. In this presentation, we report the results of large-scale mesoscopic simulations of several structurally distinct VACNT forests subjected to compressive deformation. The simulations reveal that the deformation proceeds as a phase transformation from an original low-density phase composed of vertically aligned CNT bundles to a densified phase with horizontal alignment of CNTs. The two phases are separated by a well-defined interfacial layer, which advances during the compressive deformation through localized bending and folding of nanotubes. The characteristic three-stage stress-strain dependence (an "elastic" peak followed by an extended plateau region and a sharp rise of stress in the densification regime), commonly observed in experimental probing of the mechanical properties of VACNT forests, is reproduced in all of the simulations, suggesting that the heterogeneous propagation of densification front is the general mechanism of mechanical deformation of VACNT forests.

AA.P.36
17:00
Authors : BOURDAIS Stéphane
Affiliations : IMRA EUROPE SAS 220, rue Albert Caquot 06904 Sophia-Antipolis FRANCE

Resume : The search for new photovoltaic (PV) materials by high throughput screening among crystalline materials databases - experimental or computed - is generally based on selection criteria such as optical absorption bandgap energy, Eg and majority carrier transport properties (n- or p- semiconductor type and mobility or effective mass). Unfortunately, a selection criterion is missing regarding minority carrier transport properties, especially their lifetime, that is not easily accessible from computation. Starting from the fact that the best performing photovoltaic materials (with >15% light to electricity conversion efficiency) are all crystals with perfect cubic structures, we first discuss on the possible links between photovoltaic performance, minority carrier lifetime and deviation from perfect cubic structure. Depending on the crystalline structure, cubicity can be defined as e.g. the Goldschmidt tolerance factor for perovskites or as the tetragonal distortion for Stannites, etc. Such cubicity criterion would thus be easy to derive from available computed crystalline structures, and very selective to possibly discover new absorbers for PV, LEDs or photocatalytic devices.

AA.P.37
17:00
Authors : Kisub Lim, Sung-Ho Joo, Gyu-Yeol Kim, Sang-Kyu Yoo, Je-Young Park, Jae-Wook Jeon
Affiliations : Kisub Lim, Jae-Wook Jeon College of Information and Communication Engineering Sungkyunkwan University, Suwon City 440-746, Republic of Korea; Kisub Lim, Sung-Ho Joo, Gyu-Yeol Kim, Sang-Kyu Yoo, Je-Young Park Memory Devision, Samsung Electronics Co.Ltd., Hwasung City 445-330, Republic of Korea;

Resume : In the semiconductor industries, it is necessary to develop a probe card to quickly test as many chips as possible at on the entire wafer on the time. Since a large amount of switches are not able to be mounted on the limited PCB area of probe card, the logic design of STA(Samsung Test Application) which contains 64 switches has been developed. As the automotive semiconductor products and the next generation STA require more and more switches in probe cards to shorten test times, a new format of program coding and sequences are needed. The existing coding methods require a lot of effort when detecting errors with hard coding. With over 70000 coding lines and FPGA (Field Programmable Gate Array)LUT(Look Up Table) usage, the configuration time and errors increase. This paper reports on the efficient FPGA logic to solve the problems caused by increased number of probe card switches due to multi-parallel test. We developed the verilog coding and program sequence firmware using standardization of ROM data by utilizing block memory from xilinx. We found FPGA logic utilization & configuration time reduced as the data structure becomes simple due to the use of ROM data, and it can be expected to reduce human error by coding automation. in addition, the switch configuration becomes free and scalable when designing a probe card

AA.P.38
17:00
Authors : Yurie Kim1, Jun-Yeong Jo2, Ki-Yung Kim2, and In-Gyu Choi2, and Yeong-Cheol Kim2
Affiliations : 1Department of Creative IT Engineering, POSTECH, Pohang, Republic of Korea; 2School of Energy Materials and Chemical Engineering, KOREATECH, Cheonan, Republic of Korea

Resume : Density functional theory (DFT) has become an important tool for atomic scale understanding of materials. Recently, PrBa0.5Sr0.5Co1.5Fe0.5O5-δ is receiving high attention because it shows mixed ionic and electronic conduction [1, 2]. Studying this material by DFT, however, is a big challenge because the supercell should be a reasonable size to consider the five metal elements, and there are many different atomic configurations to compute. We employed a deep neural network to obtain a neural network potential (NNP) and, therefore, to reduce the computation time by several orders of magnitude. Energy data from 2,000 atomic configurations was first obtained by DFT, and the data was enlarged to 300,000 by considering crystal symmetry, such as translation and rotation. The data was used to train and test the NNP. We will further discuss the accuracy of the NNP and ways to improve it. References [1] S. Choi, et al., Sci. Rep., 2013, 3, 2426. [2] S. Choi, et al., Nature Energy, 2018.

AA.P.39
17:00
Authors : Marcin Roland Zemła, Kamil Czelej, Piotr Śpiewak
Affiliations : Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland.

Resume : In this work, we used spin-polarized, hybrid density functional theory method to investigate the electronic structure and magneto-optical properties of various hydrogen-vacancy clusters in a diamond. Our theoretical results indicate very strong tendency toward the formation of HnV complexes up to 4 hydrogen atoms that are mostly electrically and optically active centres. One of the investigated defects introduce highly correlated electronic states that pose a challenge for density functional theory and therefore, require the special treatment when charge- and spin-density related properties are determined. We introduced an of extended Hubbard-like model of Hamiltonian with fully ab initio provided parameters to analyse the complex electronic structure of highly correlated H2V(0) defect. The role of quantum tunnelling of hydrogen in HV centre and its impact on the hyperfine structure was discussed. We demonstrate that experimentally observed HV(1-) centre is similar to well-known NV(1-), i.e. I) it possesses triplet 3A ground state and 3E excited state in C3v symmetry; II) the calculated zero-phonon line is 1.71 eV (1.945 eV for NV1-). A detailed experimental reinvestigation based on optically detected electron paramagnetic resonance spectroscopy is suggested to verify whether the HV1- centre has metastable singlet shelving states between the ground and excited state triplets and as a result, whether it may exhibit a spin-selective decay to the ground state. Acknowledgments This research was financially supported by the Polish National Science Centre under contract no. 2012/05/E/ST8/03104. Computing resources were provided by High Performance Computing facilities of the Interdisciplinary Centre for Mathematical and Computational Modeling (ICM) of the University of Warsaw under Grant No. GB69-32.

AA.P.40
17:00
Authors : Z. Skanderi1 Ilhem. R. Kriba2 A. Djebaili1*
Affiliations : 1 Laboratory of chemistry and environmental chemistry L.C.C.E - university of batna 1- Algeria 2 Faculty of Material Sciences- Department of Chemistry - University of Batna 1- 05000- Algeria

Resume : In this study, we used quantum chemistry calculations in order to determine some kinetic parameters of the isomerization reaction of the substituted tetradecahepta-ene. The studied molecules are: (C14H16, C14H8F8, C14H8Cl8, C14H8Br8 et C14H8I8) Cis and Trans. One of the adopted ways to access these parameters (activation energy, rate constant, etc ...) is looking for the transition state that is based on the exploration of intermediaries during the passage of Cis-Trans isomerization process. The study of a ten molecules series gives the following results:  The Trans conformer is more stable than the Cis. The activation energy changes very greatly depending on the size and nature of the substituent according to the reaction profile.  The constants of the isomerization reaction rates are in the following order: kC14H16 >> k C14H8F8 >> k C14H8Cl8 >>k C14H8Br8 >> k C14H8I8. The geometrical parameters vary considerably according to intermediate products The calculation methods are DFT and Ab-initio methods at STO-3G (d,p) levels Keywords: substituted tetradecahepta-ene, kinetics; isomerisation, Ab-initio, DFT

AA.P.41
17:00
Authors : Talha Qasim Ansari, San-Qiang Shi
Affiliations : The Hong Kong Polytechnic University, Kowloon, Hong Kong

Resume : Localized corrosion is one of the complex forms of corrosion which makes it difficult to detect and design-against. During metal corrosion in the corrosive environment, corrosion products are also formed as a result of electrochemical reactions inside the electrolyte. These products can precipitate on the corroding surface and stop/ slowdown the overall corrosion process. In order to understand this complex phenomenon, a multi-phase field model is proposed to simulate metal corrosion with corrosion products formation. The free energy of the system is described in terms of its metal ion concentration and the order parameters. Rather than considering linear kinetics (Allen-Cahn equation), inspired from classical rate theory, non-linear kinetics (Butler-Volmer) is considered to describe the temporal evolution of order parameters. The time dependent evolution of ionic species is governed by Nernst-Plank equations while electrostatic potential is governed by Poisson equation. The proposed model results are compared with the experimental findings and several examples are presented to show the practical applications of this model. These examples also suggest that the proposed model is, in general, not limited to corrosion process but can be a good tool for other complex phase change processes. KEYWORDS: pitting corrosion, multi-phase field model and Butler-Volmer.

AA.P.42
17:00
Authors : Kenjiro FUJIMOTO, Akihisa AIMI, Yusuke YAMADA, Shingo MARUYAMA
Affiliations : Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, Japan; Department of Applied Chemistry, School of Engineering, Tohoku University, Japan

Resume : For powder library obtained from high-throughput synthesis systems, we have developed high-speed evaluation tools for database creation. We are thinking that crystallographic data such as not only crystalline phases but also atomic coordinates and so on are necessary for prediction of new materials using machine learning. We developed a tool to efficiently measure synchrotron radiation XRD and XAFS measurements of powder libraries. Generally, in synchrotron radiation XRD powder must be filled into a thin capillary. However, our developed tool only adheres to the tape. The powder library fixed to the tape can be continuously moved to the X-ray irradiation position by the tool. By swinging the tool around the irradiation position, diffraction data close to the conventional method could be obtained. Acknowledgements: These XRD and XAFS experiments were conducted at the BL5S1 and BL5S2 of Aichi Synchrotron Radiation Center, Aichi Science & Technology Foundation, Aichi, Japan (Approval No.2017P0202).

AA.P.43
17:00
Authors : Michael Rinderle, Maximilian Speckbacher, Marc Tornow, Alessio Gagliardi
Affiliations : Department of Electrical and Computer Engineering, Technical University of Munich, Karlstrasse 45, 80333 Munich, Germany

Resume : Resistive switching devices are promising candidates for fast computer memories. Despite the simple structure of memristive elements the physical mechanisms behind the switching process are complex [1]. The kinetic Monte Carlo (kMC) method is an established model to simulate filament formation in memristive devices [2]. We present a kMC simulation to investigate the formation of silver (Ag) filaments in titanium dioxide (TiO2). We analyze under which conditions filaments form, how long the formation takes and compare the results with experimental data. The oxidation of Ag atoms at the anode, their migration through the TiO2 layer and the reduction of Ag+ ions at the cathode or in proximity to Ag atoms are modeled using an Arrhenius law. The activation energy ions have to overcome when hopping from one site to another is assumed to have a Gaussian disorder. Introducing a correlated disorder model leads to preferred pathways for Ag+ ions through the TiO2 layer and results in reduced filament formation times and allows filament formation at lower fields. [1] S. Dirkmann, et. al., J. Appl. Phys., 2015, 118, 214501 [2] S. Aldana, et. al., J. Phys. D: Appl. Phys., 2017, 50, 335103

AA.P.44
17:00
Authors : Juho Lee, 1† Hyeonwoo Yeo,1† Han Seul Kim,2 and Yong-Hoon Kim1*
Affiliations : 1 School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Daejeon, 34141, Korea 2 Center for Division of National Supercomputing Research and Development, Korea Institute of Science and Technology Information (KISTI), 245 Daehak-ro, Yuseong-gu, Daejeon 34141

Resume : While the quasi-Fermi level (or imref) is a standard concept in semiconductor physics employed to describe the finite-bias non-equilibrium operations of electronic and optoelectronic devices, its first-principles determination has not been achieved previously. Herein, based on the multi-space constrained-search density functional theory (MS-DFT) formalism we have recently developed [1], we calculate the non-equilibrium electronic structure of molecular junctions under a finite bias voltage and extract the quasi-Fermi level profiles across molecular device systems. Comparing with the conventional non-equilibrium Green’s function (NEGF) calculations based on DFT, we first confirm the practical equivalence between MS-DFT and DFT-NEGF. An important feature of MS-DFT that differentiates it from DFT-NEGF is that it relies on the determination of the quasi-Fermi level or electrochemical potentials across the channel, which are not explicitly provided within DFT-NEGF unlike their electrostatic potential counterparts. Analyzing the spatial profiles of electrochemical potentials of molecular junctions based on different electrode-molecule contact geometries [2] at varying bias voltages, we extract important insights into the nature of nonequilibrium quantum transport at the nanoscale. References [1] H. S. Kim and Y.-H. Kim, arXiv:1808.03608 [cond-mat.mes-hall]. [2] Y.-H. Kim, H. S. Kim, J. Lee, M. Tsutsui, T. Kawai, J. Am. Chem. Soc. 139, 24, 8286-8294 (2017).

AA.P.45
17:00
Authors : Sergey M. Karabanov (1), Dmitry V. Suvorov (1), Dmitriy Y. Tarabrin (1), Andrey A. Trubitsyn (1), Andrey E. Serebryakov (1), Evgeny V. Slivkin (1), Andrey S. Karabanov (2), Oleg A. Belyakov (2)
Affiliations : 1 - Ryazan State Radio Engineering University; 2 - Helios Resource Ltd.

Resume : Mathematical modeling makes it possible to reduce time and cost for the development of complex technological processes. The paper presents a complex study of the metallurgical-grade silicon purification technology by vacuum refining and plasma-chemical purification under the conditions of electromagnetic stirring of silicon melt by mathematical modeling. The paper presents the numerical models of the processes, using COMSOL Multiphysics software. The initial and boundary conditions of these processes are formed with HSC Chemistry software. To study vacuum refining under the conditions of electromagnetic stirring, mathematical models including Maxwell equations, hydrodynamics equations for incompressible liquid, mass transfer equations, including directional mass transfer and diffusion for the impurity transportation calculation inside silicon melt are used. For mathematical modeling of plasma-chemical silicon purification, HSC Chemistry software is used. For the thermodynamic estimation of the chemical processes, the change of the Gibbs free energy has been calculated. The research has shown the efficiency of using mathematical modeling for the study of complex technological processes, especially, the technology for purification of metallurgical-grade silicon to solar-grade silicon level using vacuum refining and plasma-chemical purification of silicon melt under the conditions of electromagnetic stirring.

AA.P.46
17:00
Authors : K. Pivovarova(1), M. Polyakova(1), M. Dabala'(2)
Affiliations : (1) Nosov Magnitogorsk state technical university; (2) Padova University

Resume : Nano- and ultrafinegrained structure in metals after severe plastic deformation is formed as a result of movement, accumulation, and interaction of lattice defects. After such kind of metal processing the defects concentration can be estimated by analysis of stored energy which is necessary for metal grain breaking. A method showing good results is a thermal gravimetric analysis (TG), applied together with differential thermal analysis and differential scanning calorimetry (DSC). DSC has been used to fix a temperature difference, which is in proportion to a difference in a heat flow between a reference and a sample in another crucible from the same material. TG has been used to measure changes in the specimen weight, depending on temperature at specific controlled conditions. Preliminary results showed that after combined deformational processing by drawing with bending and torsion the ultrafine grained structure was formed. On the DSC curve obtained after different kinds of plastic deformational processing the single isothermal peak in the temperature range 400-500 C was observed. With increasing of deformational processing degree the temperature of the peak formation decreased whereas the peak square, as a characteristic of stored energy, increased approximately in 1.3 times. It was connected with change of internal stresses level which increased with dislocation density growth.

AA.P.47
17:00
Authors : D. Padula, O. Omar, T. Nematiaram, A. Troisi
Affiliations : University of Liverpool, Dept of Chemistry, Liverpool, United Kingdom EMPA, Dübendorf, Switzerland

Resume : Singlet Fission is one of the possible outcomes occurring upon photoexcitation of a material in its aggregated states, where the generated singlet excited state can split in two entangled triplet states showing an overall singlet multiplicity [1]. However, only a few molecules so far have shown significant singlet fission activity [2], thus the mechanism of the process is still unclear and extracting design rules is still a challenge. Additionally, the interest in this process is also due to the possibility to generate two excitons from a photon, which is clearly beneficial for photovoltaic applications. The requirements for a material to give singlet fission are energetic in primis [3], due to the fact that, to be able to generate two triplet states from a singlet, the energy of the triplet state should be about half of the energy of the singlet state. In this contribution we present the results of a (TD)DFT protocol to screen for singlet fission materials [4]. The protocol consists in evaluating the energies of the first singlet/triplet excited states through standard computational procedures. We search publicly available databases (~1 Million materials) for potential Organic Semiconductors (OSCs) based on their computed HOMO-LUMO gap. We do this by estimating the gap from low level calculations. Once potential OSCs have been identified, we apply the protocol to evaluate whether they are promising singlet fission materials. We show the robustness of our results by re-discovering materials that are known to be singlet fission active. Additionally, we propose a high number of new singlet fission candidates that can be experimentally studied to verify the results of our predictions, and to obtain a more general view on the process to study the mechanism and extract design rules. References [1] M. B. Smith, J. Michl, Chem. Rev., 110, 6891 (2010). [2] I. Paci, J. C. Johnson, X. Chen, G. Rana, D. Popovic, D. E. David, A. J. Nozik, M. A. Ratner, J. Michl, J. Am. Chem. Soc., 128, 16546 (2006). [3] D. Casanova, Chem. Rev., 118, 7164 (2018). [4] R. Grotjahn, T. M. Maier, J. Michl, M. Kaupp, J. Chem. Theory Comput., 13, 4984 (2017).

AA.P.48
17:00
Authors : Bernardo de Souza[1], Giliandro Farias[1], Matthieu Rouzières[2], Pierre Dechambenoit[2], Fabien Durola[2], Harald Bock[2], Cristian A. M. Salla[3], Ivan H. Bechtold[3].
Affiliations : [1] Federal University of Santa Catarina, Chemistry Department, Brazil. [2] Centre de Recherche Paul Pascal, Université Bordeaux I, France. [3] Federal University of Santa Catarina, Physics Department, Brazil.

Resume : Although the phosphorescence and, to a lesser extent, delayed fluorescence of polycyclic aromatic hydrocarbons in host matrices has been studied in the middle of the last century at low as well as at room temperature, this class of materials is notably absent from the recent surge of interest in room-temperature phosphorescence (RTP) and delayed fluorescence (DF) from single-component crystalline organic materials. Recently investigated metal-free RTP and DF materials either contain heavy atoms such as bromine to facilitate singlet-triplet intersystem crossing (ISC), or polarizing heteroatoms such as oxygen or nitrogen that induce charge-transfer states, but pure hydrocarbons are absent and are even commonly assumed to not present any of these properties. Electronic transitions between non-coplanar (i.e. orthogonal or tilted) orbitals are necessary to allow for spin-orbit coupling (SOC) and thus present the aforementioned properties, however the vast majority of polycyclic aromatic compounds do not present this kind of structure. Here we describe the successful synthesis of a hydrocarbon named homotruexene and make preliminary studies on its persistent room-temperature phosphorescence and concomitant delayed fluorescence in both powder and film forms, presenting unusually high quantum yields. We study this material with both experiments and theory, using our newly developed method for computing SOC matrix elements and excited states dynamics implemented on the free software ORCA[1-2]. Here we show that it is indeed possible to explain and, to some extent, even predict these unusual properties based on theoretical grounds and detail the emission mechanisms. [1] On the theoretical prediction of fluorescence rates from first principles using the path integral approach. J. Chem. Phys. 148, 034104 (2018). [2] Submitted to J. Chem. Theory. Comp.

AA.P.49
17:00
Authors : P. Kamińska, M. Zemła, K. Czelej, P. Śpiewak
Affiliations : Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland;

Resume : Phosphorus-doped n-type diamond is currently one of the most fundamental wide bandgap materials for next generation high-power electronics and optoelectronics. Artificial diamond growth methods such as CVD involve hydrogen-containing precursors. Therefore, the hydrogen atoms can be simultaneously introduced into the diamond lattice as a contamination and form complexes with other defects. In this work, we used the spin-polarized hybrid density functional theory method to investigate the electronic structure, stability, and magnetic and optical properties of phosphorus, vacancy, and hydrogen clusters in diamond. Our results indicate a thermodynamic driving force for the formation of previously unidentified phosphorus-vacancy-hydrogen complexes that can be electrically, magnetically, or optically active centres. We found an unusual extremely large hyperfine coupling with the 31P nuclei (A > 2 GHz) for some of the investigated defects that requires further experimental verification. Finally, we demonstrate that the PV2H0 complex has two metastable triplets between the ground- and excited-state singlets, and it may exhibit a highly selective spin decay channel to a ground state, which makes the defect a promising candidate for realizing long-living solid-state quantum memory. These results provide deep insight into the donor compensation effect associated with vacancy-related clusters, and they may be useful in future identification of P-related defects suitable for quantum information processing applications.

AA.P.50
17:00
Authors : Jun-Suk Choi, Jee-Hyong Lee
Affiliations : Samsung Electronics, Sungkyunkwan University

Resume : The production difficulty of the DRAM devices is rapidly increasing due to integration process complexity and growth of the low power devices such as mobile application. These difficulties also affect product testing and yield analysis. In this study, we propose a precise way of predicting the package level yield using machine learning of imaged wafer data. We found the relationship between the wafer test data and package yield. It covered data pre-processing, feature selection and we verified the relevant data to derive an optimized relationship and the actual production process applied. There are over 200 measurement data in one chip of the wafer. The conventional way takes a long time since engineers have to investigate and judge the data themselves in order to find the causes of the failure. This leads to significant chip loss as well as man power loss in mass production. It is suggested to image a lot of data through a pre-processing process in this study. It is planning to predict package yields through machine learning of variety of data that is imaged. It is the first attempt to predict package yields through machine learning by imaging wafer data. CNN, which is easy to analyze images, was used as a machine learning tool.

AA.P.51
17:00
Authors : Camille Latouche, Adrien Stoliaroff, Stéphane Jobic
Affiliations : Institut des Matériaux Jean Rouxel − Université de Nantes, CNRS, 2 rue de la Houssinière, BP 32229, 44322Nantes Cedex 3, France

Resume : In the last years, the development of computational methods permitted to obtain a super-probe of the atomic scale. Furthermore, it is now well understood that defects in structures (few %) can either lead to better or worse performances on the targeted properties of functional semiconductors. Therefore, combining modelling and experimental procedures become crucial if one wants to fully understand a targeted material in order to improve its properties for an application. In this talk, the attention will be drawn to two buffer layers to replace CdS in CIGS devices, i. e. CdIn2S4 and In2S3 (β-phase).1–4The native point defects of both materials were investigated using DFT (GGA) together with the VASP and PyDEF codes.5,6 All the computed results were confronted to experimental data. The theoretical results fully support the observed properties and explain which defects are responsible for them, e. g. CdIn2S4 and In2S3 give n-type conductivity. Finally, computations explain why it is impossible to get p-type conductivity for In2S3. 1 E. V. Péan, N. Barreau, J. Vidal, C. Latouche, and S. Jobic, Phys. Rev. Mater. 1, 064605 (2017). 2 N. Barreau et al. Sol. RRL 1, 1700140 (2017). 3 C. Guillot-Deudon, M.T. Caldes, A. Stoliaroff, L. Choubrac, M. Paris, C. Latouche, N. Barreau, A. Lafond, and S. Jobic, Inorg. Chem. acs. inorgchem.8b01771 (2018). 4 A. Stoliaroff, N. Barreau, S. Jobic, and C. Latouche, Theor. Chem. Acc. 137, 102 (2018). 5 E. Péan, J. Vidal, S. Jobic, and C. Latouche, Chem. Phys. Lett. 671, 124 (2017). 6 A. Stoliaroff, S. Jobic, and C. Latouche, J. Comput. Chem. 39, 2251 (2018).

AA.P.52
17:00
Authors : Pascal Friederich, Reinder Coehoorn, Florian von Wrochem, Mario Ruben, Wolfgang Wenzel
Affiliations : P. F.: Department of Chemistry, University of Toronto Institute of Nanotechnology, Karlsruhe Institute of Technology; R. C.: Department of Applied Physics, Eindhoven University of Technology; F.v.W.: Sony Europe Ltd., Zn Deutschland; M.R.: Institute of Nanotechnology, Karlsruhe Institute of Technology; W.W.: Institute of Nanotechnology, Karlsruhe Institute of Technology

Resume : Small-molecule organic semiconductors are used in a wide spectrum of applications, ranging from organic light emitting diodes (OLEDs) to organic photovoltaics. A number of factors determine their charge carrier mobility, such as molecular packing, electronic structure, dipole moment and polarizability. Here, we present a multi-scale model, which provides an accurate prediction of experimental data over ten orders of magnitude in charge carrier mobility and demonstrate the de novo design of a novel organic semiconductor with improved mobility [1,2]. Molecular orientation anisotropy of molecules used in OLEDs can give rise to an enhanced light-outcoupling efficiency or to the spontaneous buildup of an electrostatic potential perpendicular to the substrate. We will present our work on the orientation anisotropy of widely used organic semiconductors using a simulation approach which mimics the physical vapor deposition process of amorphous thin films. Our simulations reveal for all studied systems significant orientation anisotropy which is in agreement with experimental results [3,4]. The availability of first-principles based models to compute key performance characteristics of organic semiconductors may enable in-silico screening of numerous chemical compounds for the development of highly efficient opto-electronic devices. [1] Friederich et al., Adv. Funct. Mater., 2016, 26 (31), pp 5757-5763 [2] Friederich et al., Adv. Mater., 2017, 29 (43), pp 1703505 [3] Friederich et al., ACS Appl. Mater. Interfaces, 2018, 10 (2), pp 1881–1887 [4] Friederich et al., Chem. Mater., 2017, 29 (21), pp 9528–9535

AA.P.53
17:00
Authors : Manav Ramprasad, Dr. Chiho Kim, Anurag Jha
Affiliations : Wheeler High School; Georgia Institute of Technology; Georgia Institute of Technology

Resume : The success of the Materials Genome Initiative [1] has led to opportunities for data-driven approaches for materials discovery. The recent development of Polymer Genome (PG), which is a machine learning (ML) based data-driven informatics platform for polymer property prediction, has significantly increased the efficiency of polymer design. Nevertheless, continuous expansion of the ‘training data’ is necessary to improve the robustness, versatility and accuracy of the ML predictions. In order to test the performance and transferability of the predictive models presently available in PG (which were previously trained on a dataset of 451 polymers), we have carefully collected additional experimental glass transition temperature (Tg) data for 871 polymers from multiple data sources. [2,3] The Tg values predicted by the present PG models for the polymers in the newly collected dataset were compared directly with the experimental Tg to estimate the accuracy of the present model. Using the full dataset of 1322 polymers, a new ML model for Tg was built following past work [4]. The RMSE of prediction for the extended dataset, when compared to the earlier one, decreased to 21.0 K from 48.7 K.To further improve the model’s performance, we are continuing to accumulate new data and exploring new ML approaches.

AA.P.54
17:00
Authors : S. K. Saida, T. K. Kundu
Affiliations : Indian Institute of Technology-Kharagpur, West Bengal, India-721302

Resume : High titania slag is one of the raw material for the production of titanium. Titania slag is produced by the carbothermic reduction of the ilmenite ore in an electrical arc furnace. In this paper, effect of the FeO, TiO2, Ti2O3 on the liquidus temperatures and viscosity of the titania slag has studied. Cooling characteristics of titania slag was performed by using the equilibrium cooling and Scheil-Gulliver cooling equations. CALPHAD approach is used for the analysis of the equilibrium calculations and the phase diagram study of different systems. Analysis shows that temperature, FeO and Ti2O3 content have the inverse relation on viscosity of slags. Cooling curve shows that, in the equilibrium cooling 1100oC is the final solidification temperature, while in Scheil-Gulliver cooling liquid phases are still existing in the room temperature. Cooling rate or step has the major influence on the final solidification temperature. Key Words: titania slag; liquidus temperatures; viscosity; CALPHAD, Scheil-Gulliver cooling curve.

AA.P.55
17:00
Authors : Awais Mahmood, Chen Shuai, Chen Chaolang, and Wang Jiadao
Affiliations : State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China

Resume : In this study, we analyze the wetting dynamics of two immiscible liquid systems with the aid of molecular dynamics simulations. An underwater oil droplet was placed on the smooth and a rough silicon surface and its wetting states were observed. The coupling parameter which defines the relative affinities between the atoms has found to have significant effect on the wetting characteristics of the oil droplet. The simulation results revealed that the solid surface became oleophobic when the coupling parameter of two liquids is kept low and the surface showed oleophilic characteristics when its value is increased. In addition, the contact angle of underwater oil droplet with the solid surface is also measured by experiments. Furthermore, the simulation and experimental contact angle data is compared with the theoretical models defined by Wenzel and Cassie. The results exhibit that for molecular dynamics simulation of two-liquid system, defining the coupling parameter is of great importance.

AA.P.56
17:00
Authors : Urmimala Dey, Nilanjan Mitra, and A. Taraphder
Affiliations : Centre for Theoretical Studies, Indian Institute of Technology, Kharagpur-721302, India; Centre for Theoretical Studies, Indian Institute of Technology, Kharagpur-721302, India, Civil Engineering Department, Indian Institute of Technology, Kharagpur-721302, India; Centre for Theoretical Studies, Indian Institute of Technology, Kharagpur-721302, India, Department of Physics, Indian Institute of Technology, Kharagpur-721302, India, School of Basic Sciences, Indian Institute of Technology, Mandi, HP 175005 India.

Resume : We investigate the existence of a body centered tetragonal (BCT) phase of Cu when single crystal FCC Cu is subjected to both high pressure and high temperature. The results have been demonstrated through DFT calculations (which are typically done at 0 K) followed by Helmholtz free energy calculations (for high temperature). The new metastable BCT phase of Cu demonstrates higher thermal conductivity compared to that of the FCC phase and thereby may be beneficial for high temperature engineering applications.

AA.P.57
17:00
Authors : D. Maouche and S. Berri
Affiliations : Laboratory for Developing New Materials and their Caracterizations, Université Ferhat Abbas UFAS1, Sétif, Algeria.

Resume : The structural, electronic and thermodynamic properties of XZrS3 (X=Ba,Sr,Ca) compounds with orthorhombic Pbnm and cubic Pm-3m phases have been investigated and reported. The calculations have been performed using various density functionals within the generalized gradient approximation (GGA). The obtained lattice parameters for Pnma phase reveal very good accord with experiment. The computed electronic band structures show that in the cubic phase the material of interest is an indirect band-gap (R-Г) semiconductor, whereas it is a direct band-gap (Г-Г) in the orthorhombic phase. The semiconducting XZrS3 (X=Ba,Sr,Ca) compounds are found to verify the stability criteria against volume change. Based on the quasi-harmonic Debye model, the thermodynamic properties of the material in question have been predicted taking into account of the lattice vibrations. The variation of the lattice constant, bulk modulus, heat capacity, Debye temperature and thermal expansion coefficient as a function of pressure in the range 0-30 GPa and temperatures of 0-1500 K is computed. Our findings show that external effects such as temperature and pressure are highly effective in tuning some of the macroscopic properties of the compounds under study. Keywords: Chalcogenide perovskite; Phase stability; Electronic Properties; Thermodynamic properties; Ab–initio calculations.

AA.P.58
17:00
Authors : Te-Hua Fang*, Chen Fang-Yi
Affiliations : Department of Mechanical Engineering, National Kaohsiung University of Science and Technology, Kaohsiung 80778, Taiwan

Resume : In this study, molecular dynamics (MD) was used to simulate a single layer of germanene quantum dots. The mechanical properties of buckled honeycomb germanene quantum dots under tension were investigated at different temperatures. The results show that Young's modulus of germanene quantum dots in armchair and zigzag directions at a temperature of 300 K are about 169 and 154 GPa, respectively. The ultimate strength of the single layer germanene in armchair and zigzag directions are 8.9 and 15.4 GPa, respectively. As the temperature was increased from 100 to 500 K, the ultimate strength and Young's modulus were significantly decreased. The ultimate strength of the single layer germanene in zigzag and armchair directions decreased about 65.8% and 66.6%, respectively. The results of this investigation are helpful for the application of two-dimensional germanene as optoelectronics and semiconductor-topological insulators.

AA.P.60
17:00
Authors : Yiran Ying, Xin Luo, Haitao Huang
Affiliations : a. Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, P.R. China b. School of Physics, Sun Yat-sen University, Guangzhou, Guangdong Province, P.R. China

Resume : Electrocatalytic reduction of nitrogen to ammonia, as an alternative to the energy-consuming Habor–Bosch nitrogen fixation, is a fascinating yet challenging topic. Here, by means of density functional theory and ab initio molecular dynamics calculations, we design a novel group of materials—two-dimensional (2D) pentagonal transition metal phosphides (penta-MP, M=Ti, Zr, Hf) and study their potential applications in the nitrogen fixation. Penta-MP are predicted to have dynamical, thermal, and mechanical stabilities. Their quasi-planar crystal structures and metallic properties facilitate the strong N2 adsorption on their surface. Gibbs free energy diagram suggests that NRR on penta-MP prefers the distal reaction mechanism, with the low overpotential of 0.56 eV for penta-TiP, which can benefit efficient electrocatalytic nitrogen fixation. Our findings open up a new pathway for designing novel 2D materials as well as electrocatalysts.

AA.P.60
17:00
Authors : Yuefeng Hu,Xiu Li Si, Xiaoling Wu, Guo An Cheng,and Rui Ting Zheng
Affiliations : College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, PR China

Resume : In this paper, we study the solar selective absorbing properties of metal nanowire array (NWA)/ anodic aluminum oxide (AAO) composites at 1000K via numerical simulation. The materials and structural parameters which influence the wavelength absorption between 0.28 and 10 μm are simulated and optimized. The results reveal that W NWA/AAO composites with nanowire length of 7.3 μm, fill factor of 0.03, and AAO template thickness of 0.1μm exhibits the best selective absorption. This composite has solar absorptivity α = 0.90 and thermal emissivity ε = 0.045 in 1000K, and shows a photothermal conversion efficiency of 71.5%. The effect of materials and structural parameters on the photothermal conversion efficiency was detailed discussed in this paper.

AA.P.61
17:00
Authors : Wen-Yi Tong, Eric Bousquet, and Philippe Ghosez
Affiliations : Theoretical Materials Physics, Q-MAT, CESAM, University of Liege (B5), B-4000 Liege, Belgium

Resume : For the clean (001) surface of silicon, owing to a lack of upper bonding partners, each atom has two single occupied dangling bonds pointing out of the surface. Pairs of Si atoms dimerize, using up one dangling bond per atom to form the dimer bond. By depositing SrTiO3, the structural complexity of both the ferroelectric SrTiO3 itself and the buffer layers offers the possibility to break the "dimer-row" reconstruction of Si atoms. In this work, we systematically investigate SrTiO3/Si heterostructures from first-principles modeling in order to contribute to a thorough understanding of the driving force for this issue. Using first-principles density functional theory calculations, we firstly analyze the influence of the buffer layer on structural and electronic properties of the Si layers. It is proved that Si layers with full monolayer Sr coverage is the key to break Si dimers. Based on this point, we test all the possible SrTiO3/Si heterostructures with one monolayer Sr buffer layer to see how defective surfaces affact on Si dimers. The polarization of SrTiO3 layers and the distance between interface Sr and Si are sensitive to the surface configurations, which are the two main factors for whether the surface Si atoms prefer to dimerize or not. Using a parallel plate capacitor model, the effects mentioned above are well understood. Furthermore, our calculations show that for the cases with silicon dimers, the heterostructures possess semiconducting behavior. However, when the dimer is broken, the systems become metallic. Such an interesting phenomenon has been explained through detailed analysis of electronic states. This work helps to a fundamental understanding of the important role played by interfacial and surface structures in the SrTiO3/Si heterostructures and indicates the possibility to realize metal-insulator transition in such systems. It may suggest guidelines for the future design of coupled functional oxide-semiconductor devices in nanaotechonology.

AA.P.62
Start atSubject View AllNum.Add
 
Quantum materials 1 : -
08:30
Authors : Alex Zunger
Affiliations : University of Colorado

Resume : The existence of finite and large band gaps in binary (NiO, MnO, FeO, CoO) and ternary 3d oxides (such as YTiO3, YVO3, LaVO3, CaMnO3, LaMnO3, LaFeO3, CaFeO3, YNiO3, YCoO3) has help the condensed matter community in constant fascination ever since Mott and Peirles have proposed the famous model of two correlated electrons on a single 3d site as the origin of the Mott gap. This mechanism established such oxides as strongly correlated systems and precluded the use of single determinant, mean-field models (such as Density functional theory) as a tool for understanding the electronic structure of such important technological materials. Indeed, whereas the low temperature AFM phases were described successfully long ago in DFT by allowing unit cell doubling and spin-polarization, the recurring argument has been that this description will fail for the paramagnetic phase (PM) that was viewed by naïve DFT practitioners as non magnetic, thus predicting zero gap even though experimentally they have large band gaps. We show that in many such cases of N-DFT (Naïve DFT) applications it was not the lack of correlation in the theoretical description that caused failure in predicting the right trends. Instead, it was the interpretation of the PM phases as having zero spin on an atom-by-atom basis, rather than having a zero total spin. Once this is fixed, we find that using proper DFT the binary and ternary oxides listed above have gaps both in the AFM and the PHM phases, and, at the same time, the crystal structures and octahedral distortions are correctly described. Moreover, similar results are obtained in DFT even without using an inter-electronic Hubbard U Repulsion. This suggests that the mechanism of gapping in Mott insulators may not be the Mott mechanism, but actually symmetry breaking describable by DFT. Now that wide gap 3d oxides are legitimately gapped in DFT, we can turn to consequences. The fact that a given compound manifests integer ratios between its component elements (“the law of definite proportions”) has been the cornerstone of our understanding of formal oxidation states (taking up integer values), and defect physics (showing that violation of integer ratios by formation of defects costs energy and is thus unlikely at low temperatures). We point out an interesting class of exceptions to this universal understanding, whereby a degenerate insulator with Fermi energy (EF) inside the conduction band (“Transparent Conductors”) could form massive concentration of metal vacancies that cost no energy to form. I will discuss how this leads to a surprising series of crystallographic “ordered vacancy compounds” and to a “knob” allowing us to balance conductivity vs transparency in TCO’s. * In collaboration with G. Trimarchi, J. Varignon and M. Bibes and funded by US DOE, Office of Science.

AA.4.1
09:00
Authors : Jose J. Plata, Javier Amaya Suárez, Antonio M. Márquez, J. Fdez. Sanz
Affiliations : Universidad de Sevilla, Department of Physical Chemistry, Faculty of Chemistry, E-41012, Sevilla, Spain

Resume : The application of ferroelectric materials in solar cells has recently attracted the attention of the scientific community because of the coupling of light absorption with other functional properties. In conventional solar cells, the solar cell power conversion efficiency (PCE) is constrained by the Shockley-Queisser limit, in which the excited carriers are separated by the internal electric field at a p-n junction or other material interface. However, ferroelectrics present an intrinsic spontaneous polarization that is an alternative way to separate charge by the bulk of the material defined as bulk photovoltaic effect. Ferroelectric oxides, as perovskites, are stable in a wide range of mechanical, chemical and thermal conditions and can be synthesized using low-cost techniques. On the other hand, these oxides usually present band gaps located higher in energy that the solar spectrum. However, new promising perovskites oxides based materials have been designed absorbing in the solar spectrum using doping techniques or applying strain. For instance, the growth of a thin layer of a perovskite on top of a substrate with different lattice parameters creates a strain that modifies its electronic properties. However, the epitaxial growth of a material on top of a substrate is not trivial and presents different requirements. Formation energies, elastic strain energy or topological information are some of the properties that should be evaluated to discern what material and plane is an optimal candidate to be the substrate of another material. Here, we present a high-throughput search of potential substrate-ferroelectric systems and the study of their electronic properties.

AA.4.2
09:15
Authors : Ulrik Grønbjerg Vej-Hansen, Line Jelver, Peter Mahler Larsen, Daniele Stradi, Søren Smidstrup, Karsten Wedel Jacobsen, Kurt Stokbro
Affiliations : Synopsys Denmark Aps, Fruebjergvej 3, DK-2100 Copenhagen, Denmark; Synopsys Denmark Aps, Fruebjergvej 3, DK-2100 Copenhagen, Denmark and Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark; Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark; Synopsys Denmark Aps, Fruebjergvej 3, DK-2100 Copenhagen, Denmark; Synopsys Denmark Aps, Fruebjergvej 3, DK-2100 Copenhagen, Denmark; Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark; Synopsys Denmark Aps, Fruebjergvej 3, DK-2100 Copenhagen, Denmark

Resume : In this work, we present a general method to determine the low-strain interfaces between two crystalline materials. The method finds all possible interfaces between the two materials and identifies the strain and area of corresponding 2-dimensional coincidence cells for a given set of Miller indices. This allow one to identify and generate interface configurations of interest for atomic-scale simulations, for example interface coincidence cells that combine a small cross section with a relatively small interface strain. This is especially relevant for electron transport simulations using the non-equilibrium Green’s function (NEGF) method, where computational speed depends critically on the device cross section. We apply the method to a technologically relevant interface between the two materials CZTS(e) and CdS, used in photovoltaic devices. Previous studies have shown that the detailed properties of this interface are quite important for the overall performance of the photovoltaic device. Specifically, it has been found that CZTS gives rise to interface states, leading to band gap narrowing and associated lowering of the open-circuit voltage. It is shown that if sulfur is replaced with selenium, these states do not appear, and the device characteristics are improved.

AA.4.3
09:30 Coffee break    
 
Quantum materials 2 : -
10:00
Authors : Oleg V. Yazyev
Affiliations : Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

Resume : A large number of diverse topological electronic phases that can be realized in materials have been predicted recently. We have developed a high-throughput computational screening methodology for identifying materials hosting various topological phases among known materials. The entire dataset of results obtained using this high-throughput search is now publicly available via the Materials Cloud platform [1]. In my talk, I will focus on several predictions resulting from this search that have been successfully confirmed by experiments. A new Z2 topological insulator was theoretically predicted and experimentally confirmed in the β-phase of quasi-one-dimensional bismuth iodide Bi4I4 [2]. The electronic structure of β-Bi4I4, characterized by Z2 invariants (1;110), is in proximity of both the weak TI phase (0;001) and the trivial insulator phase (0;000). We further predicted robust type-II Weyl semimetal phase in transition metal diphosphides MoP2 and WP2 characterized by very large momentum-space separation between Weyl points of opposite chirality [3]. Recent experiments on WP2 revealed record magnitudes of magnetoresistance combined with very high conductivity and residual resistivity ratio [4], and many other extraordinary properties. This work was supported by the Swiss NSF, ERC project “TopoMat” and NCCR Marvel. 1. G. Autès, Q. S. Wu, N. Mounet, and O. V. Yazyev, “TopoMat: a database of high-throughput first-principles calculations of topological materials”, https://www.materialscloud.org/discover/topomat 2. G. Autès et al., Nature Mater. 15, 154 (2016). 3. G. Autès, D. Gresch, M. Troyer, A. A. Soluyanov and O. V. Yazyev, Phys. Rev. Lett. 117, 066402 (2016). 4. N. Kumar et al., Nature Commun. 8, 1642 (2017).

AA.5.1
10:30
Authors : Thomas Pope Werner A Hofer
Affiliations : School of Natural and Environmental Sciences, Newcastle University, Newcastle NE1 7RU, United Kingdom

Resume : An extended electron model fully recovers many of the experimental results of quantum mechanics while it avoids many of the pitfalls and remains generally free of paradoxes. The formulation of the many-body electronic problem here resembles the Kohn-Sham formulation of standard density function theory. However, rather than referring electronic properties to a large set of single electron orbitals, the extended electron model uses only mass density and field components, leading to a substantial increase in computational efficiency. We present a proof-of-concept practical implementation of this method and show it reproduces the accuracy of more widely used methods on a test-set of small atomic systems, thus paving the way for the development of fast, efficient and accurate codes on this basis.

AA.5.2
10:45
Authors : Hong Seok Kang, Tekalign Terfa Debela, Hafiz Ghulam Abbas
Affiliations : Department of Nano & Advanced materials, Jeonju University, Republic of Korea; Institute of Advanced Materials, Jeonju University, Republic of Korea; Department of Nanoscience and Nanotechnology, Jeonbuk National University, Republic of Korea.

Resume : Based on a combination of various first-principles methods, we propose various kinds of layered materials. One is tetragonal GeP2, which has optimal band offset for photocatalyzed CO2 decomposition in wide pH range. The second one is TeSe2, which exhibits phase polymorphism, interesting spin texture, and ferroelectricity. The third one is orthorhombic BP3charactierized by high electron mobility. Next, a combined experimental and theoretical collaboration is described for an efficient photoelectrochemical (PEC) water splitting of p-GeAs/n-Si heterojunction based on the band alignment, buildup of space charge in the junction, and the band bending of the n-Si at the electrolyte interface. Third, our extensive DFT calculation complemented by analyses of charge transfer, band structure analyses, and Volmer-Heyrovsky reactions give a deep insight into experimental results, which has shown that the 1T'-phase guest-intercalated MoS2 nanosheets synthesized by one-step hydrothermal reaction exhibit excellent stability as well as higher catalytic activity toward the hydrogen evolution reaction. Finally, our extensive ab initio molecular dynamics simulation not only reproduces experimental voltage-charge capacity curves for WS2@nitrogen-doped graphite composites in lithium ion battery but also gives us a detailed picture on the structural evolution in the charge-discharge process.

AA.5.3
11:15 PLENARY SESSION 1    
12:30 Lunch    
 
Artificial intelligence 1 : -
13:45
Authors : George E. Froudakis*
Affiliations : Department of Chemistry, University of Crete, Voutes Campus, GR-71003 Heraklion, Crete, Greece * frudakis@uoc.gr

Resume : A novel Machine Learning (ML) methodology is applied for investigating the storage of various gases (H2, CH4, CO2) in 140.000 MOFs. From our previous experience in this recently developed subfield of Artificial Intelligence we concluded that there are 2 major factors that play dominant role in the accuracy of the model: The size of the training set and the quality of the predictors [1]. Up to now the basic structural characteristics of MOFs i.e. organic linkers, metal clusters, etc. have been mainly used as predictors. This results in minimum transferability of the model and demands a large training data base. Aiming at both, the transferability of our model and the reduction of the training data set, we introduce 2 different classes of predictors, based on fundamental chemical and physical properties: Atom Types, and Atom Probes. The main difference from previous models is that our predictors are based on the chemical character of the atoms which consist the skeleton of the materials and not their general structural characteristics. With this bottom up approach we go one step down in the size of the predictors employing chemical intuition. Our results clearly showed that both targets were accomplished resulting in a universal ML model that can be transformed in different kind of materials, too. References: Froudakis et.al, Chemically-intuited, large-scale screening of MOFs by machine learning techniques, Nature Computational Materials 3:40(2017)

AA.6.1
14:15
Authors : Michael Rinderle, Jonas Lederer, Waldemar Kaiser, Alessio Gagliardi
Affiliations : Department of Electrical and Computer Engineering, Technical University of Munich, Karlstrasse 45, 80333 Munich, Germany

Resume : Getting accurate performance predictions of organic semiconductors is crucial for the development of organic devices. Existing multi-scale analysis often relies on computationally expensive quantum-chemical calculations [1]. Machine learning approaches have been proposed to efficiently predict quantum-chemical quantities [2]. In this project, we present a multi-scale simulation for charge transport in an amorphous organic thin film of pentacene. The molecular structure of the pentacene film is obtained by Molecular Dynamics simulations. The transfer integrals between molecules are calculated with Density Functional Theory (DFT) methods and passed to a kinetic Monte Carlo simulation to calculate charge carrier mobility. Since DFT simulations for every possible molecule orientation are not feasible we use machine learning using kernel ridge regression to predict the transfer integrals [3]. One critical step to obtain a well trained, highly predictive model is the feature design for the molecular structure. We use different geometric features like distance, orientation, and curvature, as well as electrical features such as the Coulomb matrix. By coarse-graining the molecules we study how the number of features can be reduced. We compare the predictive power of the trained model for different feature designs. [1] J. Kirkpatrick, et. al., PRL, 2007, 98, 227402 [2] K. Hansen, et. al., J. Chem. Theory Comput. 2013, 9, 3404 [3] J. Lederer, et. al., Adv. Theory Simul. 2018, 102, 1800136

AA.6.2
14:30
Authors : Anastasiia Doinychko, Nicolas Onofrio
Affiliations : Laboratoire d’informatique de Grenoble, Université Grenoble Alpes, Grenoble, France; Department of Applied Physics, The Hong Kong Polytechnic University, Hong Kong SAR

Resume : Machine learning methods are well known to be used for solving problems related to artificial intelligence, computer vision, and network security. More recently, machine learning has been applied to predict the state of an atomic system. For example, an atomic environment can be mapped into a vector which can be used by a learning model to train and predict the corresponding physical property (i.e. the energy of the fragment, the local force on the atom, etc.). The main objective of the present work is to study such a technique in order to accelerate the performance of large-scale atomistic simulations with accuracy approaching that of quantum mechanical calculations. We propose a simple feed-forward neural network interatomic potential to predict the local force on atoms and we describe its implementation in a molecular dynamics code. The proposed model was trained against first principle calculations to described the interactions of elemental Aluminum with chemical accuracy, comparable to previous kernel-based machine learning framework. More importantly, we show how to systematically extend the model to describe binary systems via hierarchical training.

AA.6.3
14:45
Authors : Karine ABGARYAN
Affiliations : Dorodnicyn Computing Centre, Federal Research Center “Computer Science and Control” of Russian Academy of Sciences

Resume : The multiscale scientific problems are formulated including modeling the phenomena of incomparable spatial and / or temporal scales when solution cannot be achieved without taking into account all the factors that play key roles. The basic principles of the developed information technology for constructing multiscale models with the use of such new concepts as "basic model-composition" and "Multiscale Composition" are presented. For their description a set theory techniques are used. On the actual class of problems for new semiconductor materials it is shown that such an approach can be used in the study of multiscale physical processes or phenomena when the problem arises of combining existing models related to different space/time levels in a computational process.

AA.6.4
15:00
Authors : Luca M. Ghiringhelli
Affiliations : Fritz Haber Institute of the Max Planck Society

Resume : The number of possible materials is practically infinite, while only few hundred thousands of (inorganic) materials are known to exist and for few of them even basic properties are systematically known. In order to speed up the identification and design of improved, new, and even novel optimal (functional) materials for a desired property or process, strategies for quick and well-guided exploration of the materials space are highly needed. A desirable strategy would be to start from a large body of experimental or theoretical data, and by means of “(big-)data-analytics” methods, to identify yet unseen patterns or structures in the data. This leads to the identification of maps (or charts) of materials where different regions correspond to materials with different properties. The main challenge on building such maps is to find the appropriate descriptive parameters (called descriptors) that define these regions of interest. Here, I will present a suite of artificial-intelligence methods, recently developed by us for the machine-aided identification of descriptors and materials maps. These methods are applied to, e.g., crystal-structure prediction, the metal/nonmetal classification, the prediction of novel 2D and 3D topological insulators, and the construction of a tolerance factor for the stability of perovskites, enabling the costless prediction of thousands of new candidate perovskites. I will also describe the infrastructure to perform such analyses online, via the "Big-data-analytics toolkit" within the framework of the Novel-Materials-Discovery (NOMAD) Laboratory.

AA.6.5
15:30
Authors : Tong-Yi Zhang
Affiliations : Materials Genome Institute, Shanghai University, Shanghai, China

Resume : This presentation briefly introduces the concept of materials informatics, which is growing extremely fast by integrating artificial intelligence and machine learning with materials science and engineering, where techniques, tools, and theories drawn from the emerging fields such as data science, internet, computer science and engineering, and digital technologies, are applied to the materials science and engineering to accelerate materials, products and manufacturing innovations. Preliminary works about the data-driven development of a formula of time, stress, and temperature dependent deformation (creep and stress relaxation) and the Bayesian statistical analysis of the size-dependent strength of concrete are introduced here to illustrate the concept of materials informatics, where sufficient data are necessarily prerequisites. Building-up materials database is urgent. In addition to the financial support from funding agents, every member in the materials community shall be willing to share his/her own experimental and/or computation data.

AA.6.6
15:45
Authors : Thomas Soini, Ole Carstensen, Fedor Goumans
Affiliations : Software for Chemistry & Materials

Resume : Material properties are ultimately determined at the atomistic level, and a bottom-up approach to modeling and simulation is increasingly becoming an integral part of materials discovery and design. Materials design can be improved by making more rational choices based on insights from electronic structure and atomistic calculations. High-throughput screening of calculated properties can accelerate materials discovery by focusing on the most promising materials, vastly reducing the experimental search space. Since researchers and business have been more exposed to simulations, they are more aware of the limitations and possibilities of the different models, which is crucial to successfully employ computations to advance materials innovation. In the context of materials design by computation, we will discuss current capabilities and ongoing developments in the Amsterdam Modeling Suite (AMS), developed by Software for Chemistry & Materials (SCM) in Amsterdam. AMS offers a comprehensive suite of atomistic modeling tools at the electronic structure level (DFT and tight-binding methods) and faster potential-based methods, including reactive force fields (ReaxFF). The AMS driver has advanced potential energy surface and molecular dynamics capabilities which can easily extended to other atomistic codes through a flexible interface. Relevant applications in batteries, solar cells, 2D electronics, organic electronics, and polymers will be discussed. We will also discuss upcoming advances in catalysis modeling: the major chemical companies will improve the entire reactor design in the EU-project ReaxPro, led by SCM. We will coordinate the coupling of atomistic models for individual reactions to mesoscale methods for reaction rates in the full chemical network and finally to macroscale models for reactive fluid dynamics. Such a truly, full multi-scale modeling approach has great potential to several other application areas in materials science.

AA.6.7
16:00 Coffee break    
 
Artificial intelligence 2 : -
16:30
Authors : Fedwa El-Mellouhi
Affiliations : Qatar Environment and Energy Research Institute (QEERI), Hamad Bin Khalifa University, Qatar Foundation, P.O. Box 34110, Doha, Qatar.

Resume : The computer-aided design of materials has witnessed important progress over the past few years. This being said, it depends crucially on the crystal structure and the polymorphs considered. I will show how we considered various polymorphism to obtain new stable and undiscovered compounds based on the assessment of the relative stability of various phases with respect to a reference structure. These calculations rely on the calculation of the thermodynamic stability by computing the convex hull energy aided by open-source computational databases. I will also summarize some of our recent findings using DFT combined with machine learning to perform a systematic analysis of the structure-to-property relations exploring fully inorganic ABC3 chalcogenide (I-V-VI3), halide (I-II-VII3) and some hybrid perovskites. The analysis focused on the role of BC6 octahedral deformations, rotations and tilts over the thermodynamic stability and optical properties of the compounds. Machine learning algorithms helped to estimate the relations between the octahedral deformation and the bandgap, and established a similarity map among all the calculated compounds. We propose that compositions grouped together on the similarity map are amenable to form mix-ion compounds, offering interesting guidelines on how to engineer mix-phase perovskites. This work have been supported by the Qatar National Research Fund (QNRF) through the National Priorities Research Program (NPRP8-090-2-047).

AA.7.1
17:00
Authors : Dr. Alisa Stratulat
Affiliations : Carl Zeiss Microscopy

Resume : The design and discovery of new advanced materials relies on the understanding of the material structure (phases, porosity), properties (mechanical, thermal) and performance (corrosion resistance, reliability). To further advance materials research and improve industrial processes, it is essential to extract quantitative, actionable information from micrographs, understand grain size distribution, shape, porosity and layer interface integrity. The challenge can now be met with microscopy-optimized machine learning for image segmentation to enhance material research and bring innovation in materials design. Machine learning image segmentation for 2D and 3D datasets will be described. ZEISS ZEN Intellesis provides an additional tool for industrial materials researchers interested in getting more insights from their data: a data-agnostic machine learning system that can be used alone or in conjunction with other software platforms and generate intelligently pre-trained models for each data set. ZEN Intellesis has the capability to segment large sets of single or multi-channel data generated using any microscopy method in 2D and 3D by applying the pre-trained model. This presentation will overview the advantages of using machine learning image segmentation in several example cases; performing grain size analysis on metals or ceramics, exporting real 3D structures for physics simulations, determining the size distribution of nanoparticles in agglomerates and performing layer, porosity and phase analysis of materials.

AA.7.2
17:15
Authors : Nicola Stehling, Robert Masters, Martina Azzolini, Maurizio Dapor, Cornelia Rodenburg
Affiliations : NS, RM, CR: Department of Materials Science and Engineering, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD MA, MD: European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) Strada delle Tabarelle, 286, I-38123 Villazzano TRENTO (TN)

Resume : Large multidimensional image data sets have become commonplace in advanced materials characterisation which has led to a sharp increase in the use of machine learning analysis workflows, in order to be able to isolate definite trends which may not have been clear in smaller data sets or due to human bias in data interpretation. However, it can be difficult to link the outputs obtained in this way to the underlying materials properties. In our work we collect spatially resolved secondary electron energy emission spectra into Secondary Electron Hyperspectral Image (SEHI) data sets using a wide range of different materials [1]. As SEHI has not yet been widely exploited partly due to a lack of understanding on what gives rise to spectral features, we seek to understand the information encoded in such data sets. To do so we applied a principal component analysis (PCA) approach [2] and validation against conventional spectroscopy and Monte Carlo Modelling. Going forward we will continue to use this approach with the aim to advanced materials characterisation for complex materials systems in which function is strongly dependent on subtle local variations in chemistry as is the case in many complex men made and natural materials systems [3–5]. We will also address the prospect of developing an experimental database across different materials, equipment and collection parameters to see the bigger picture within large data and share findings within a community with emphasis on how such data might be used for modelling.

AA.7.3
17:30
Authors : Alfred Ludwig
Affiliations : Institute for Materials, Faculty of Mechanical Engineering, Ruhr University Bochum, Bochum, Germany

Resume : Discovery of new materials is a key challenge in materials science: e.g. new materials for the sustainable production/storage/conversion of energy carriers are necessary to improve existing and to enable future energy systems. Efficient methods for discovery and optimization of new materials are necessary: Here the thin-film combinatorial materials science approach is presented as an effective means to produce large datasets on new materials. This approach is useful for validation of theoretical predictions (e.g. from high-throughput computations), and production of large, consistent and complete experimental datasets which can be used by computational materials scientists. The approach comprises fabrication and processing of thin-film materials libraries by combinatorial sputter deposition processes and optional post-deposition treatments (e.g. thermal oxidation, annealing, dealloying), followed by the high-throughput characterization of the different thin-film samples contained in these libraries, and finally the organization of the acquired multi-dimensional data in adequate databases as well their effective computational analysis and visualization. The importance of defining adequate screening parameters and according designs of materials libraries is addressed. High-throughput material characterization methods are automated, fast, and mostly non-destructive: examples are EDX and RBS for composition, XRD for crystal structure, temperature-dependent resistance for phase transformation, high-throughput test stands for optical properties (color, transmission) and mechanical properties (stress, hardness, elastic modulus), and scanning droplet cells for photoelectrochemical properties screening. The obtained results for up to quinary systems are visualized in the form of composition-processing-structure-function diagrams, interlinking compositional data with structural and functional properties. The talk will cover and discuss examples of combinatorial discoveries and development of new materials. Examples include shape memory alloys, multiple principal element alloys, multinary nanoparticles, and metal oxide thin film materials libraries for solar water splitting.

AA.7.4
18:00
Authors : Quan Qian
Affiliations : School of Computer Engineering & Science, Shanghai University, Shanghai, China 200444 Materials Genome Institute, Shanghai University, Shanghai, China 200444

Resume : Machine learning is increasingly regarded as an effective way for modern materials design and development. Generally, we use different machine learning algorithms, for instance, supervised learning or unsupervised learning, to train a model based on the history samples, and then use the model to predict the unknown properties under certain specific conditions, such as materials compositions and processing parameters. Although such kind of machine learning applications are sometimes useful, how to guide materials scientists to design the next experiment more likely to get the good results is more important. That is to say, what we really want machine learning to do is not only predicting the results, but also guide your action. In this talk, combining with specific materials examples, I will focus on Bayesian optimization method to measure the uncertainty among different experiments design. On top of that, under the trade-off between model exploration and exploitation, I will discuss the detailed process of how to use Bayesian optimization to obtain your optimized object step by step.

AA.7.5
18:15
Authors : Marcin Roland Zemła (1), J. S. Wróbel (1), C.-C. Fu (2), F. Soisson (2), T. Wejrzawnoski (1)
Affiliations : (1) Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland. (2) DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France

Resume : Grain boundaries (GBs) are immanent components of crystal structure of the structural materials, such as e.g. Fe-Cr steels. Moreover, they have considerable influence on materials properties and in particular mechanical strength. Since, grain boundary is a defect with energy higher than the grain interior, most of temperature induced processes are intensified there. One of the phenomena which is of high importance in a proper understating of bcc Fe-Cr steels is segregation of Cr to GBs. In a current study, we investigated the segregation process of Cr atoms at Fe-Cr tilt GBs. The spin-polarized density functional theory (DFT) calculations of bulk system and Σ5(310) tilt GB were performed. The fluctuation of magnetic moments, chemical potentials, and formation energies of point defects were studied as a function of distance from GB’s plane. The Nudged Elastic Band method was applied to determine migration barriers of Fe, Cr and a vacancy. The established database was used to parameterize the Atomistic Kinetic Monte Carlo (AKMC) model which allowed to obtain Langmuir-McLean segregation isotherms. The predications of the AKMC model are compared with existing atomic-scale experiments. Acknowledgments This work was carried out with the support of the Interdisciplinary Centre of Mathematical and Computational Modelling (ICM) University of Warsaw under grant no. G62-1 and no. GA65-14.

AA.7.6
18:30
Authors : Qing Hou, Alexey A. Sokol, John Buckeridge, Scott M. Woodley, C. Richard A. Catlow
Affiliations : Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ

Resume : We present a consistent interatomic force field for indium sesquioxide (In2O3) and tin dioxide (SnO2) that has been derived to reproduce lattice energies and, consequently, the oxygen vacancy formation energies in the respective binary compounds. The new model predicts the dominance of Frenkel-type disorder in SnO2 and In2O3, in good agreement with ab initio defect calculations. The model is extended to include free electron and hole polarons, which compete with charged point defects to maintain charge neutrality in a defective crystal. The stability of electrons and the instability of holes with respect to point defect formation rationalizes the efficacy of n-type doping in tin doped indium oxide (ITO), a widely employed transparent conducting oxide in optoelectronic applications. We investigate the clustering of Sn substitutional and oxygen interstitial sites in ITO, finding that the dopants substitute preferentially on the cation crystallographic d site in the bixbyite unit cell, in agreement with experiment. The force field described here provides a useful avenue for investigation of the defect properties of extended transparent conducting oxide systems, including solid solutions.

AA.7.7
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Quantum materials 2 : -
08:30
Authors : Kristjan Haule
Affiliations : Rutgers University, USA

Resume : Materials with strong electronic correlations have long resisted abinitio modeling due to their complexity arising from non-perturbative strength of the interaction. The Dynamical Mean Field Theory in combination with the Density Functional Theory has changed this position, and enabled detailed modeling of the electronic structure of correlated solids such as heavy fermions, transition metal oxides and iron superconductors. Our recent theoretical development of forces on all atoms in the unit cell [1,2] allows one to predict very accurately the structural changes and movement of the atoms in the solid across the Mott metal-insulator transition from first principles, and the coupling between the electronic and lattice degrees of freedom in correlated solids. The precision of the method will be demonstrated on the example on the Mott transition in rare-earth nickelates[2], and prediction of the anomalous large electron-phonon coupling in FeSe superconductor [3], which was recently experimentally verified[4]. While these methods are very successful, their implementation is not numerically exact, and still rely on the fact that correlations in solids are short ranged. Recent advances in Monte Carlo summation of high-order Feynman diagrams allowed one to obtain essentially exact solution of several quantum models subject to on-site Coulomb repulsion, while the long-range Coulomb repulsion in solids remained a challenge. Very recently we developed the Variational Diagrammatic Monte Carlo method [5], which sums up all Feynman diagrams, and gives numerically exact solution in classical model of solids, the uniform electron gas at metallic densities. Its efficiency paves the way for controlled simulations of electronic structure from first principle in moderately correlated solids in not too distant future. [1] Forces for Structural Optimizations in Correlated Materials within DFT+Embedded DMFT Functional Approach, Kristjan Haule and Gheorghe L. Pascut, Phys. Rev. B 94, 195146 (2016). [2] Mott Transition and Magnetism in Rare Earth Nickelates and its Fingerprint on the X-ray Scattering, Kristjan Haule, Gheorghe L. Pascut, Scientific Reports volume 7, Article number: 10375 (2017). [3] Strong pressure-dependent electron-phonon coupling in FeSe, Subhasish Mandal, R. E. Cohen, and K. Haule, Phys. Rev. B 89, 220502(R) (2014). [4] Femtosecond electron-phonon lock-in by photoemission and x-ray free-electron laser, Gerber S, Z.X.Shen, et.al., Science 357, 6346 (July 2017). [5] Feynmann’s solution of the quintessential problem in solid state physics, Kun Chen and Kristjan Haule, arXiv (2018).

AA.8.1
09:00
Authors : Ji-Sang Park
Affiliations : Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, UK

Resume : Imperfections are categorized into point defects and extended defects depending on whether the translational symmetry is locally broken or not, respectively. The computational methodologies to investigate point defects have been thoroughly documented, and some research groups already made their codes for automatic calculation of defects public. Calculation methods for investigation of extended defects, however, require further development to overcome the difficulties like the large degree of structural freedom and the large computational size. We propose a strategy based on a genetic algorithm to find the stable and/or metastable atomic structure of extended defects like grain boundaries [1]. By applying the strategy, we succeeded to reproduce the previously known structures of grain boundaries in CdTe [2,3]. We also found that grain boundaries can be stabilised further by breaking the mirror symmetry. Our grain boundary models do not have deep recombination centre as a result of reconstructions. We expect that our approach can be easily employed to study extended defects in other materials. [1] Ji-Sang Park, Stabilization and self-passivation of symmetrical grain boundaries by mirror symmetry breaking, Phys. Rev. Materials 3, 014602 (2019). [2] Y. Yan, M. Al-Jassim, and K. Jones, Journal of Applied Physics 94, 2976 (2003). [3] C.-Y. Liu, Y.-Y. Zhang, Y.-S. Hou, S.-Y. Chen, H.-J. Xiang, and X.-G. Gong, Physical Review B 93, 205426 (2016).

AA.8.3
09:15
Authors : Piotr Kucia
Affiliations : Department of Chemistry, Imperial College London

Resume : Theoretical investigation of oxygen defects in highly hydrogenated graphene, synthesised by Birch reduction Graphene is a material with superb electronic properties, due to its highly regular structure there is almost no electron scattering, once current passes through, what results in very high electric conductivity. Because of that, it is very interesting material for use instead silicon in electric transistors, however one thing that prevents its use is lack of band gap. One of the promising approaches to introduce band into graphene is to chemically functionalise it with hydrogen. Unfortunately, there is currently no method of synthesis of fully hydrogenated graphene. The method that was most successful is based on Birch reduction and gives extent of hydrogenation close to 100%, however with some functional groups containing carbon bonded oxygen. It is not known exactly what kind of functional group they are, and what type of effect do they have on properties of the material. In this research Density Functional Theory will be used to predict what are those functional groups, how do they alter electronic and magnetic properties of hydrogenated graphene and how can synthesis method be altered in order to control quality of final product.

AA.8.4
09:30
Authors : C. Ricca, I. Timrov, M. Cococcioni, N. Marzari, and U. Aschauer
Affiliations : Department of Chemistry and Biochemistry and National Centre for Computational Design and Discovery of Novel Materials MARVEL, University of Bern, CH-3012 Bern, Switzerland; Theory and Simulation of Materials (THEOS) and National Centre for Computational Design and Discovery of Novel Materials MARVEL, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; Theory and Simulation of Materials (THEOS) and National Centre for Computational Design and Discovery of Novel Materials MARVEL, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; Theory and Simulation of Materials (THEOS) and National Centre for Computational Design and Discovery of Novel Materials MARVEL, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; Department of Chemistry and Biochemistry and National Centre for Computational Design and Discovery of Novel Materials MARVEL, University of Bern, CH-3012 Bern, Switzerland;

Resume : Motivated by indications that strain and defects can stabilize a ferromagnetic ground state in normally antiferromagnetic SrMnO3 thin films, we use DFT+U calculations to investigate the interplay between oxygen vacancies (VO), strain, and magnetism in this material. We applied for the first time self-consistent site-dependent (SC-SD) DFT+U, since defect formation in transition-metal oxides induces local perturbations in the chemical environment of Hubbard sites around the defect that may not be properly described by applying a global U value on all sites as in conventional DFT+U. U is treated as an intrinsic response property of the material and computed using density-functional perturbation theory starting from a DFT ground state by an iteration of perturbing all inequivalent Hubbard sites followed by geometry relaxation with the determined U values until convergence of the geometry and U. Already for the stoichiometric material, using a SC U increases the accuracy of lattice parameter predictions, which is crucial to study strain-induced changes in properties, while the site-dependence of U around a defect has a strong impact on the computed formation energies and consequently on all related properties. As such USCSD prevents overestimating the stability of the ferromagnetic order thanks to a proper description of excess charge localization upon defect formation and helps in rationalizing different ordering of VO depending on the magnetic order in the epitaxial thin film.

AA.8.5
09:45
Authors : Reetu Joseph, Carlos Jiménez, Dmitry Busko, Damien Hudry, Guojun Gao, Andrey Turshatov, Ian Howard, and Bryce Richards
Affiliations : Reetu Joseph; Carlos Jiménez; Dmitry Busko; Damien Hudry; Guojun Gao; Andrey Turshatov; Ian Howard; Bryce Richards Institute of Microstructure Technology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany Ian Howard; Bryce Richards Light Technology Institute, Karlsruhe Institute of Technology, Engesserstrasse 13, 76131 Karlsruhe, Germany

Resume : Upconversion (UC) is a process in which radiation of lower energy is converted to higher energy. We focus on energy transfer UC (ETU) in micropowders doped with Er3+ activators and Yb3+ sensitizers. We study a series of host materials (namely: NaYF4, YF3 and La2O3), with the same doping concentration. We measure the visible upconversion emission intensity as a function of 980 nm excitation power density. An analytical model is proposed to describe the excitation power density dependence of these ETU processes in which two lower energy photons are combined to form a higher energy photon. In addition to describing the entire dependence of UC, the model yields a critical power density (CPD) which can be used as a figure of merit for comparing the excitation power density required for upconversion to become efficient in a given material. The model predicts that the lifetime of the first excited state, namely 2F5/2 of Yb3 plays a major role in determining the excitation power dependence of the efficiency of two-photon ETU as confirmed by lifetime measurements at 990 nm with 980 nm excitation. The model also gives insight into the pathway through which different ETU processes are achieved. For example, in the host YF3, the model yields the same CPD for the green emissions (520-570 nm) and near infrared (NIR) emissions (820-870 nm) proving that these NIR emissions are caused by the same green levels radiatively relaxing into the 1550 nm level of Er3+ instead of the ground state.

AA.8.6
10:00 Coffee break    
 
Materials by design (batteries) : -
10:30
Authors : Axel Groß
Affiliations : Institute of Theoretical Chemistry, Ulm University, and Helmholtz Institute Ulm, 89081 Ulm/Germany

Resume : Descriptors can be defined as fundamental materials properties that are correlated to critical performance parameters of these materials. One of the most prominent descriptors has been established in the field of electrocatalysis. It has been shown that the binding energy of oxygen atoms on metal electrodes can be directly related to the activity of the oxygen reduction reaction (ORR) [1] which is one of the crucial reactions in fuel cells and metal-air batteries. Once a descriptor has been established, in can be very beneficial in the materials design process as in a first step promising candidates can be identified based on the computation of just one materials property. On the other hand, the existence of just one descriptor can also limit the room for materials improvements, as will be demonstrated using the ORR as an example. The growth of dendrites is one of the major concerns in battery operation as it leads to a reduction in battery performance and also represents a crucial safety problem. Here we will show, based on first-principles electronic structure calculations, that the height of metal self-diffusion barriers may serve as a descriptor for the occurrence of dendrite growth in batteries [2]. Thus they can act as the basis of a guiding principle for the design of safer battery electrodes. [1] J.K. Norskov et al. , J. Phys. Chem. B 108, 17886 (2004). [2] M. Jäckle, K. Helmbrecht, M. Smits, D. Stottmeister, and A. Groß, Energy Environ. Sci. 11, 3400 (2018).

AA.9.1
11:00
Authors : Leonid Kahle, Nicola Marzari
Affiliations : Theory and Simulation of Materials (THEOS), and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland

Resume : A comprehensive screening of structural databases for ionic conductors by means of atomistic simulations can identify novel candidates for next-generation solid-state lithium-ion batteries, and deepen our understanding of the microscopic processes and structural motifs governing ionic diffusion in the solid state. This task is challenging because no classical simulation potential is predictive for wide varieties of materials classes, and first-principles simulations struggle to reach the necessary timescales. To model ionic diffusion efficiently and accurately, we derive a novel hybrid quantum/empirical model that can be used efficiently for molecular dynamics simulations of solid-state diffusion [1], by applying some simple and intuitive approximations to fully self-consistent density-functional theory. This models underpins our high-throughput screening efforts for Li-ion conductors, powered by the AiiDA materials informatics [2] platform. We will present the different screening stages, show how high-level workflows can be used to automate and optimize the calculation of transport coefficients, and provide first results on promising candidates. [1] L. Kahle, A. Marcolongo, N. Marzari, Phys. Rev. Materials 2, 065405 (2018) [2] G. Pizzi etal, Comput. Mater. Sci. 111, 218-230 (2016)

AA.9.2
11:15
Authors : Jin Hyun Chang, Juan Maria García-Lastra, Tejs Vegge
Affiliations : Department of Energy Conversion and Storage, Technical University of Denmark; Department of Energy Conversion and Storage, Technical University of Denmark; Department of Energy Conversion and Storage, Technical University of Denmark

Resume : A new class of cathode materials for Li-ion batteries such as lithium transition metal oxyfluorides (Li2TMO2F) [1,2] exhibit considerably higher capacity compared to conventional LiCoO2 and LiFePO4. Despite their merits, they suffer from a fast capacity fading upon cycling. Such a limitation calls for an in-depth investigation of how these materials behave at different lithiation levels. Li2TMO2F has a disordered structure, which makes it virtually impossible to study all the configurations directly using ab initio methods such as Density Functional Theory (DFT), even if one limits the cell size relatively small. Cluster Expansion [3, 4] is an effective method to study materials with a large configurational space. Using our recently developed CLuster Expansion in Atomic Simulation Environment (CLEASE) code [5], we demonstrate how one can model both thermodynamic and transport properties using the cluster expansion formalism based on DFT and Nudge Elastic Band (NEB) calculations. 1. R. Chen et al., Adv. Energy Mater., 5, 1–7 (2015). 2. R. Chen et al., RSC Adv., 6, 65112–65118 (2016). 3. J. M. Sanchez, F. Ducastelle, and D. Gratias, Phys. A, 128, 334–350 (1984). 4. J. M. Sanchez, Phys. Rev. B, 81, 224202 (2010). 5. J. H. Chang et al., arXiv preprint arXiv:1810.12816, 2018.

AA.9.3
11:30
Authors : Stefano Sanvito
Affiliations : School of Physics and CRANN, Trinity College Dublin Ireland

Resume : The development of novel materials is a strong enabler for any technology, and often technology and materials innovation cannot be separated. Unfortunately the process of finding new materials, optimal for a given application, is lengthy, often unpredictable and has a low throughput. Here I will describe a systematic pathway to the discovery of novel materials, which demonstrates an unprecedented throughput and discovery speed. The method can be applied to any materials class and any potential application. I will use the example of magnetism to introduce the main features of the method, and I will demonstrate the discovery of several new high-performance magnets. Furthermore, I will highlight how such high-throughout schemes can be combined with machine-learning methods for data-mining to extract novel materials designing rules and for identifying new prototypes for further investigation. Based on an extensive electronic structures library of Heusler alloys containing 236,115 prototypical compounds, we have filtered those alloys displaying magnetic order and established whether they can be fabricated at thermodynamical equilibrium [1]. Specifically, we have carried out a full stability analysis for intermetallic Heuslers made only of transition metals. Among the possible 36,540 prototypes, 248 are found thermodynamically stable but only 20 are magnetic. The magnetic ordering temperature, T_C, has then been estimated by a regression calibrated on the experimental T_C of about 60 known compounds. As a final validation we have attempted the synthesis of a few of the predicted compounds and produced two new magnets. One, Co2MnTi, displays a remarkably high T_C in perfect agreement with the predictions, while the other, Mn2PtPd, is a complex antiferromagnet. In the second part of my talk I will discuss the use of machine-learning methods for predicting the Curie temperature of ferromagnets, based solely on their chemical composition, and for sorting magnets into hard and soft [2]. In particular I will discuss how to develop meaningful feature attributes for magnetism and how these can be informed by experimental and theoretical results. Our work paves the way for large-scale design of novel magnetic materials at unprecedented speed. [1] Stefano Sanvito, Corey Oses, Junkai Xue, Anurag, Tiwari, Mario Zic, Thomas Archer, Pelin Tozman, Munuswamy Venkatesan, J. Michael D. Coey and Stefano Curtarolo, Accelerated discovery of new magnets in the Heusler alloy family, Science Advances 3, e1602241 (2017). [2] S. Sanvito, M. Zic, J. Nelson, T. Archer, C. Oses and S. Curtarolo, Machine Learning and High-Throughput Approaches to Magnetism, In: Andreoni W., Yip S. (eds) Handbook of Materials Modeling. pp. 1-23, Springer, Cham (2018)

AA.9.4
12:00
Authors : Aquil Ahmad*, S. K. Srivastava and A. K. Das
Affiliations : Department of Physics, Indian Institute of Technology, Kharagpur, India-721302

Resume : Heusler alloys are the material of interest to the scientific community since decades, as they are proficient in many fields like Half-metals i.e. they show 100% spin polarization near Fermi level, spin gapless semiconductors (SGS), topological insulators and ferromagnetic shape memory alloys (FSMA) [1,2]. They are potential candidate for spintronics and magnetic refrigeration technology due to their high magnetization and Curie temperature. Co2 based full Heusler alloy specially Co2FeAl (CFA) has been investigated theoretically as well as experimentally but very few reports are available in Fe2-based Heusler alloys, so we did a systematic study on the phase stability, site preference and the electronic structures of Fe2CoAl (FCA), which will be helpful to design new functional materials in these series of the alloys. In case of full- Heusler alloy, so-called X2YZ type of compounds, there are four Wyckoff positions available, namely A (0, 0, 0), B (0.25, 0.25, 0.25), C (0.5, 0.5, 0.5) and D (0.75, 0.75, 0.75), respectively. Here, different site occupations of X and Y atoms result in two different types of ordered structure so-called L21-type (Cu2MnAl prototype) under space group Fm-3m and XA-type (Hg2CuTi prototype) under space group F-43m. The later one is also known as, Inverse-Heusler Alloy. All calculations have been performed using a computational code WIEN2k, which is based on full potential linear augmented plane waves (FP-LAPW) method developed by Blaha et al. [3]. To find out the most stable ground state of FCA alloy we have considered all possible ordered structures under Ideal L21 (Cu2MnAl prototype) and XA (Hg2CuTi prototype) ordering. From total energy versus volume curve, we observed that XA type structure (Hg2CuTi prototype) is energetically more favorable than L21 (Cu2MnAl prototype) structure; particularly XA-I type structure. We have calculated total energies E (Ry) of XA and L21 type Fe2CoAl (FCA) alloy as a function of the cell volume (E-V curve). In our calculations, ferromagnetic (FM) and non-magnetic (NM), and antiferromagnetic (AFM) states were considered for FCA alloy to achieve the most stable ground state. The total density of states (T-DOS) for all cubic FCA structures is calculated at their equilibrium lattice constants under GGA and GGA+ U approximation. We observed that FCA alloy is metallic in all type of possible structures; in particular XA-I ordered structure, a band gap for the down spin channel is observed near Fermi level (EF), which is a signature to be a half-metallic ferromagnets (HMF). Moreover, GGA+ U (Coulomb potential) is essential when dealing with such kind of highly correlated system. A band gap for the spin down channel of 0.8 eV was observed under GGA+ U which was underestimated by GGA. Comparing the total up and down electrons densities, we have noted that the differences of the total magnetic moment Mt (µB/f.u.) of this material is due to the difference in up and down electron no at Fermi level (EF). The down spin DOS is gradually increased for all cases, whereas those of the up-spin DOS remains unchanged. From our results, we conclude that the Fe2CoAl alloy is not a perfect half metal in any configurations but still can be used as a good spin polarised material for spintronics application; further, Fermi level could be tune in the middle of the spin down gap by applying a hydrostatic pressure in terms of lattice constant “a” variations with respect to their optimized lattice constant a0. REFERENCES [1] R. A. de Groot, F. M. Mueller, P. G. v. Engen, and K. H. J. Buschow, Physical Review Letters 50, 2024 (1983). [2] M. Jourdan et al., Nature communications 5, 3974 (2014). [3] P. Blaha, K. Schwarz, G. K. Madsen, D. Kvasnicka, and J. Luitz, An augmented plane wave local orbitals program for calculating crystal properties (2001). [4] J. P. Perdew, K. Burke, and M. Ernzerhof, Physical review letters 77, 3865 (1996).

AA.9.5
12:15
Authors : Aquil Ahmad1*, S. K. Srivastava, A. K. Das
Affiliations : Department of Physics, Indian Institute of Technology, Kharagpur-721302 India

Resume : Heusler Alloys (HAs) are basically an X2YZ type of compounds where X and Y are transition metals and Z represents main group element, are generally called full-Heusler alloys [1]. These materials are useful in many fields like spin gapless semiconductors, ferromagnetic shape memory alloys, half-metallic ferromagnets, and topological insulators [2,3]. HAs are said to be half-metallic ferromagnets (HMF), i.e., 100% spin-polarized near Fermi level from band structure calculations. Their properties can be tuned easily by a slight change in composition, atomic ordering and hence the reason of attraction of researchers across the world. Proficient literature based on experimental as well as theoretical work is available related to Co2 based Heusler alloys, however, very few reports are available if it comes to devices compatibility under uniform strain and tetragonal distortions are applied, in this direction we have thoroughly investigated Co2FeAl alloy by means of first-principles calculation using WIEN2k code based on FPLAPW method. We have also investigated the relative phase stability, electronic structures, and magnetic states stability. To start the calculation, we have taken our experimental lattice constants of 5.72 Å, obtained from our experimental work based on Co2FeAl Heusler alloy nanoparticles, and after volume optimization, we got optimized lattice constant of 5.703 Å. Initially, the calculation was started from zero strain in CFA having a lattice constant of 5.703 Å and then strains were applied as -6%, -5%, -4%, -3%, -2%, -1%, 0, up to 6% relative to the optimized lattice constant. Generally, in a layered structure, an epitaxial strain is expected from its adjacent layers that is why we studied the effects of tetragonal distortion with c axis which was varied from -6% to 6% relative to the equilibrium value by keeping total volume of the cell constant. Our results reveal that Co2FeAl alloy is a half-metallic ferromagnet (HMF) under strong interaction between transition metals and hence forming a calculated total magnetic moment of 5.0 µB/f.u. We also have shown that, in Co2FeAl, Co has a local magnetic moment of 1.23 µB and Fe of 2.81 µB, Al has a spin moment of -0.047. The calculated spin-polarized total density of states plot (TDOS) exhibits a gap of 0.11 eV at Fermi level (EF) for the case of minority spin electrons and conducting for majority electrons. The gaps centers are changed due to strain with respect to the Fermi level, Egap also slightly changed with respect to EF but the general shapes of the total DOS not. We have calculated spin polarization (P), as the ratio [D↑(EF) -D↓(EF)] / [D↑(EF) D↓ (EF)], where D↑(EF) and D↓(EF) are the majority and minority density of states (DOS) at EF, respectively. P, This study will open-up a paradigm to design such functional material for the application of spintronics as well as magnetic refrigeration technology. Keywords: Heusler alloy, Slater-Pauling rule, Half- metallicity. References [1] T. Graf, C. Felser, and S. S. Parkin, Progress in solid state chemistry 39, 1 (2011). [2] R. De Groot, F. Mueller, P. Van Engen, and K. Buschow, Physical Review Letters 50, 2024 (1983). [3] M. Jourdan et al., Nature communications 5, 3974 (2014).

AA.9.6
12:30 Lunch    
 
Materials by design (semiconductors) : -
14:00
Authors : Zhe Liu1*, Nick Twyman1,2*, Felipe Oviedo1, Z. Ren3, S.I.P. Tian3, Sara Bonner1, Shijing Sun1, Benji Maruyama5, Pieremanuele Canepa6, Aron Walsh2, Vladan Stevanovic4, Tonio Buonassisi1
Affiliations : 1 Massachusetts Institute of Technology, Cambridge, MA 02139, USA 2 Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom 3 Singapore-MIT Alliance for Research and Technology, 138602 Singapore 4 Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, USA 5 Air Force Research Laboratory, Dayton, Ohio 45433, USA 6 National University of Singapore, 119077 Singapore *Equal contributors

Resume : Early-stage materials-discovery efforts often focus on a single “performance-based” parameter of merit, such as solar-cell efficiency and battery energy/power density [1]. Nevertheless, the industrial scale-up and adoption of a novel material also depends on its “manufacturability” (ability to be mass produced in an industrial setting) and “reliability” (performance over time). Manufacturability and reliability can be challenging to quantify. In this study, we attempt to define, measure, and quantify manufacturing-relevant parameters, then screen for them using high-throughput materials search tools. We demonstrate initial experimental screenings on the basis of these manufacturing-relevant parameters. We posit that multi-objective materials design is possible and needed, to accelerate the transition of new materials from lab to fab [2]. [1] R.E. Brandt et al., MRS Communications 5, 265 (2015). [2] J.-P. Correa Baena et al., Joule 2, 1410 (2018).

AA.10.1
14:30
Authors : Mariana Kozlowska, Xiaojing Liu, Michael Adams, Ian Howard, Lars Heinke, Wolfgang Wenzel, Christof Wöll
Affiliations : Institute of Nanotechnology; Institute of Functional Interfaces; Institute of Microstructure Technology, Karlsruhe Institute of Technology (KIT), 76344 Eggenstein- Leopoldshafen, Germany

Resume : Due to their large photoabsorption coefficients for visible light, porphyrin derivatives are widely used in light-harvesting applications, such as photovoltaics and photocatalysis. Numerous studies have been reported on porphyrin thin films deposited on solid substrates. They were also integrated into surface-anchored metal-organic frameworks (SURMOFs) of highly ordered structure, resulting in photovoltaic activity of MOF, their photostability and sensitizing function in photon upconversion. Here, we use quantum mechanical calculations in order to explain highly efficient excited-state transport properties of porphyrin SURMOF with Pd-coordinated organic linkers [1]. The calculated transfer rates are consistent with experimentally obtained rates, which result in micron-range exciton diffusion length in this MOF. First principle calculations are also applied to understand mechanism of charge transport in Zn-coordinated porphyrin-containing SURMOFs with embedded fullerene molecules [2]. The improved photoconductivity is shown to be derived from the spatially continuous network of donor and acceptor domains in MOF material. Owing to the fact that the porphyrin properties can be tailored by advanced organic chemistry and MOF properties can be tuned for the specific applications, ab initio calculations enable valuable predictions of new promising candidates for light harvesting. [1] M. Adams, M. Kozlowska, N. Baroni, M. Oldenburg, R. Ma, D. Busko, A. Turshatov et al., Highly efficient 1D triplet exciton transport in a Pd-porphyrin based SURMOF, submitted. [2] X. Liu, M. Kozlowska, T. Okkali, S. Bräse, W. Wenzel, C. Wöll, L. Heinke et al., Molecular photon-cunduction in thin film of metal-organic frameworks, submitted.

AA.10.2
14:45
Authors : Anuj Goyal, Vladan Stevanović
Affiliations : Colorado School of Mines, Golden, CO 80401, USA

Resume : Despite decades of efforts, achieving p-type conductivity in the wide band gap ZnO in its ground- state wurtzite structure continues to be a challenge. Here we detail how p-type ZnO can be realized in a known metastable, high-pressure rocksalt phase (also wide-gap) with Li as an external dopant. Using modern defect theory, we predict Li to dope the rocksalt phase p-type by preferentially sub- stituting for Zn and introducing shallow acceptor levels, resulting in predicted hole concentrations to exceed 10^19 cm(^−3). Formation of compensating donors like interstitial Li and unintentional hydrogen, ubiquitous in wurtzite phase, is inhibited by the close-packed nature of the rocksalt polymorph. Also, relatively high absolute valence band edge of rocksalt ZnO benefits low hole effective masses and hole delocalization. In addition to the technological significance, our results reveal polymorphism as a promising route to overcome strong doping asymmetry of wide band gap oxides. Reference: A. Goyal, V. Stevanović, Phys. Rev. Mater. 2 084603 (2018)

AA.10.3
15:00
Authors : Lijun Zhang
Affiliations : School of Materials Science and Engineering, Jilin University, Changchun 130012, China

Resume : Semiconductor materials are widely used in many optoelectronic applications such as solar cell, photo-detector, light-emitting diode, photocatalysis, etc. Discovery of new optoelectronic semiconductors via rational design is of crucial importance for making breakthrough enhancement of materials performance in applications. With dramatically increasing computing capability of supercomputers and continuously developed computational algorithms, people can resort to materials simulation to explore the properties of thousands of potentially useful materials in a fraction of time that the real experiments might take. This makes theoretical design of functional materials with desired properties in computers come true. In this talk depending on time I will present our development on open-source Python framework designed for large-scale high-throughput energetic and property calculations, the Jilin University Materials-design Python Package (Jump2) and our recent work on computational materials by design for optoelectronic semiconductors (e.g., solar absorbers, transparent conductors, photodetection and light-emitting semiconductors, etc.).

AA.10.4
15:30
Authors : Ramya Kormath Raghupathy, Hendrik Wiebeler, Ram Kuchana, Thomas D. Kühne, and Hossein Mirhosseini
Affiliations : Dynamics of Condensed Matter and Center for Sustainable Systems Design, Chair of Theoretical Chemistry, University of Paderborn, Warburger Str. 100, D–33098 Paderborn, Germany

Resume : A promising and cost-effective route to boost the efficiency of solar cells is to stack individual solar cells into tandem cells: the efficiency of a two sub-cell tandem can be raised up to 42% [1]. A tandem cell consists of several layers that are either mechanically stacked or monolithically integrated. Monolithic tandems consists of sub cells which are electrically connected by a tunnel junction/recombination layer. Each layer in a tandem should have specific properties such as appropriate band gap and conductivity. In addition, the absorber and tunnel junction layer should be dopable. In this work, we have performed high-throughput screening to identify promising materials that can be employed in tandems as absorbers and tunnel junction. We have screened binary and ternary non-oxide semiconductors from Materials Project database [2]. Our aim is to find non-toxic compounds with appropriate band gap and electrical conductivity. Defect physics calculations were performed to investigate the dopability of compounds and those compounds which uphold these defects will be discussed during the presentation. [1] A. De Vos, J. Phys. D: Appl. Phys., 1980, 13, 839 [2] A. Jain, S.P. Ong, G. Hautier, W. Chen, W.D. Richards, S. Dacek, S. Cholia, D. Gunter, D. Skinner, G. Ceder, K.A. Persson, APL Materials, 2013, 1, 011002

AA.10.5
15:45
Authors : Prashun Gorai, Robert McKinney, Andriy Zakutayev, Vladan Stevanovic
Affiliations : Colorado School of Mines, National Renewable Energy Laboratory, Golden, CO 80401, USA.

Resume : Power electronics are used to control and convert power in a wide range of products from consumer electronics to large-scale industrial equipments. While Si-based power devices account for the vast majority of the market, more efficient materials such as SiC, GaN, and Ga2O3 are starting to gain grounds. Yet, these emerging materials face challenges due to high synthesis costs or poor thermal properties. The time is ripe to start exploring beyond these handful of materials. The power electronic figure of merit (FOM) of a material can be rapidly assessed with modern computational methods and models. Here, we present the first-ever broad computational exploration to identify novel materials for next-generation power electronics. We utilized ab initio methods in conjunction with semi-empirical and phenomenological models of transport properties and critical breakdown field, respectively, to compute the Baliga FOM of 1176 oxides, sulfides, nitrides, carbides, silicides, and borides that are reported in the ICSD and exhibit finite calculated band gaps. In addition to correctly recognizing known power electronic materials, the exploration has revealed promising candidates that warrant detailed computational and experimental investigations.

AA.10.6
16:00 Coffee break    
 
Materials by design 1 : -
16:30
Authors : Julien Vidal
Affiliations : EDF R&D, Department MMC, Les Renardières, F-77250 Moret sur Loing, France

Resume : Principal components of Nuclear Power Plants (NPP) experience ageing phenomena over the course of several decades of typical operation. In particular, irradiation induced embrittlement of steels constitutive of Reactor Pressure Vessel (RPV) are constantly assessed over the course of NPP lifetime through surveillance programs eventually leading to implementation of operation margins to ensure sufficient safety. Complementary to this action, development of predictive tools based on either statistical approach or physically informed models are also required. Considering typical RPV steel, no less than 5 different solute species are necessary to be accounted for to properly address material ageing mechanism, making it a combinatorial problem to solve. Atomistic calculations are employed to generate data on solute-point defect interactions then used in multi-scale modelling tools covering multiple space and time scales. In this presentation, different aspects relevant to the material database and its use as model input (representativity of the data, temperature effect, use of machine learning) will be presented. Finally, multi-scale models and methodology to assess their relevancy will be detailed in the case of RPV steel embrittlement.

AA.11.1
17:00
Authors : Goran Vukelic, Josip Brnic
Affiliations : University of Rijeka, Faculty of Maritime Studies, Rijeka, Croatia; University of Rijeka, Faculty of Engineering, Rijeka, Croatia

Resume : This paper presents a comparison of five AISI 300 series stainless steels (304, 314, 316L, 316Ti, 321), commonly used in marine industry. Steels are compared based on experimentally determined and numerically predicted mechanical properties. Afterwards, change of some of the properties is predicted using regression analysis. Experimentally, stress-strain curves are determined at several temperatures (20°C, then in 200-700°C range with a 100°C step) and from them ultimate tensile (UTS) and yield (YS) strengths extracted. A creep test is performed to investigate creep behavior in the same range of elevated temperatures. Charpy test is performed to determine materials’ impact resistance. Numerically, single specimen test method is simulated and FE stress analysis results are used to calculate J-integral to quantify crack driving force. Comparing the results, it can be noted that 304 has the highest YS and UTS at room temperature but at the elevated temperatures it is outperformed by other steels (e.g. 316Ti). As for the creep behavior, it can be noticed that 316Ti and 321 have relatively better creep resistance at very high temperatures than the rest of the group. On the basis of experimentally obtained results, change of the mechanical properties is predicted. Curves are fitted through the experimental data points and, by means of regression analysis, equations are given that can be used to predict the change of UTS, YS and modulus of elasticity as a function of temperature. This is done first for every single steel and afterwards for a tested group gaining single equation that should cover whole series. Using this approach, change of mechanical properties is predicted for AISI 303 and the results show decent agreement between these values and available experimental ones.

AA.11.2
17:15
Authors : Gauthier Lefevre, Sebastien Saitzek, Rachel Desfeux, Adlane Sayede
Affiliations : Univ. Artois, CNRS, Centrale Lille, ENSCL, Univ. Lille, UMR 8181 – UCCS – Unité de Catalyse et Chimie du Solide, F-59000 Lille, France

Resume : Hydrogen is a promising energy carrier, compatible with the sustainable energy concept. In this field, solid-state hydrogen-storage is a key challenge in developing hydrogen economy. The capability of absorption of large quantities of hydrogen makes intermetallic systems of particular interest. Light metals, especially magnesium, possess a high gravimetric hydrogen density but not the capabilities of good kinetic and absorption/desorption process. Improvement of these can be achieved by magnesium based alloys and in this context, theoretical prediction of new structures would be useful to orient prospective experimental synthesis. In this work, efforts have been devoted to the theoretical investigation of binary systems with pressure consideration. An efficient prediction of stable alloys under pressure for magnesium-based system was performed at ab initio level. The effect of pressure change radically the minimal energy compositions and various rich-Mg compounds were found. Results are in agreement with recent exploration and new synthesis methods. For interesting alloys, a careful investigation of potential hydrides has been performed, and electronic properties denote interesting informations on hydrogen atom behaviour in magnesium-based alloys. Results are giving attractive insights on identifying destabilized metal hydrides and encouraging the use of similar work to design hydride systems.

AA.11.3
17:30
Authors : R. V. Belosludov [1], O. S. Subbotin [2,3], R. K. Zhdanov [2,3], Yu. Yu. Bozhko [2,3], K. V. Gets [2,3], Y. Kawazoe [4], V. R. Belosludov [2,3]
Affiliations : [1] Institute for Materials Research, Tohoku University, Sendai, Japan [2] Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia [3] Novosibirsk State University, Novosibirsk, Russia [4] New Industry Hatchery Center, Tohoku University, Sendai, Japan

Resume : The strategy to realize highly selective guest adsorption is based on the properties of the guest molecules, control of the host structure and understanding of the structure-property relationships. The theoretical methods has significant potential to support the experimental exploration of novel storage materials. Theoretical model for calculating the thermodynamic properties of nanoporous materials with weak guest-host interactions was realized. The proposed model accounted for multiple cage occupancy, host lattice relaxation, and the description of the quantum nature of guest behavior. Thus, the thermodynamic stability of various gas hydrates were studied using the proposed model and obtained results are in agreement with available experimental data [1-3]. For evaluation the parameters of weak interactions, a TDDFT formalism and local density technique entirely in real space were implemented for calculations of vdW dispersion coefficients within the all-electron mixed-basis approach. The combination of both methods enables one to calculate thermodynamic properties without resorting to any empirical parameter fittings. The formation of CO2/CH4, CO2/N2 and CO2/N2/CH4 hydrates were studied. It was found that at high nitrogen concentration in CO2/N2 gas mixture, carbon dioxide can replace methane in the hydrate phase at temperatures and pressures of the permafrost regions or below the seafloor, since the phase stability of binary CO2/N2 hydrate is similar to pure CH4 hydrate [4]. REFERNCES 1. R. V. Belosludov et al. J. Phys. Chem. C 118 (2014) 2587. 2. R. V. Belosludov et al. Fluid Phase Equlibria 413 (2016) 220. 3. O. S. Subbotin et al. Phys. Chem. Chem. Phys. 20 (2018) 12637. 4. V. R. Belosludov et al. Molecules 23 (2018) 3336.

AA.11.4
17:45
Authors : Rafaela-Maria Giappa1*, Emmanuel Klontzas 1, 2 , Emmanuel Tylianakis3 and George Froudakis1
Affiliations : 1 Department of Chemistry, University of Crete, Voutes Campus, GR-71003 Heraklion, Crete, Greece 2 National Hellenic Research Foundation, V. Constantinou Ave. 48, 11635, Athens, Greece 3 Department of Materials Science and Technology, University of Crete, Voutes Campus, GR-71003 Heraklion, Crete, Greece * rafaelagiappa@gmail.com

Resume : Since water in the form of vapour and droplets in the atmosphere is estimated to be about 13 thousand trillion litters, there has been a great challenge on harvesting atmospheric water in different humidity conditions. Metal Organic Frameworks (MOFs) serve as promising candidates for harvesting water from air by adsorption over a wide range of humidity values. Since many MOFs include benzene rings in their organic linkers, we strategically functionalized 40 benzene molecules and studied their interaction with water by using accurate quantum chemistry methods (RI-MP2/def2-TZVPP). Our results indicate that the water interaction with several substituted benzenes (-CONHNH₂, -NHCOCH₃, -C(OH)₃, -CONH₂, -SOOH, -SO₃H, -OSO₃H, -OLi) can be up to five times stronger with respect to the corresponding unsubstituted benzene. In addition, Grand Canonical Monte Carlo simulations revealed that the storage performance of selected MOFs with functionalised organic linkers was significantly enhanced over the unfunctionalised ones. Since many MOFs include benzene rings in their organic linkers, our results can be used to guide further experimental work on water harvesting applications.

AA.11.5
18:00
Authors : C. Guedj1, L. Jaillet2, S. Redon3
Affiliations : 1 Univ. Grenoble Alpes, CEA, LETI, 38000 Grenoble, France 2 Univ. Grenoble Alpes, CNRS, Inria, Grenoble INP*, LJK, 38000 Grenoble, France *Institute of Engineering Univ. Grenoble Alpes 3 OneAngstrom, https://www.oneangstrom.com

Resume : Hydrogen is a major chemical element used in the semiconductor industries, but its analysis at the atomic scale is still challenging. H processes are strategic for etching, cleaning, passivating dangling bonds prior to epitaxy, or performing the smartcut™ process [1], therefore a precise understanding of H-induced defectivity is useful to unravel the reactional mechanisms and to optimize critical technological steps. Now, the rapid pace of industrial innovations in sub-3 nm CMOS technologies can benefit from a high-throughput and realistic modelling of H-based defects. Here we investigate the interaction of hydrogen with carbon nanostructures using the Brenner [2],[3] module of the SAMSON software platform (https://www.samson-connect.net), in comparison with published experimental and theoretical data. These results provide the necessary building blocks to obtain an atomistic database of H defects for analyzing the structure and energetics of hydrogenated carbon nanostructures. [1] M. Bruel, Electronics Letters, vol. 31, p. 1201 (1995) [2] D.W. Brenner, Phys. Rev. B, 42, 9458 (1990) [3] D.W. Brenner and al., J. Phys.: Condens. Mater. 14, 783 (2002)

AA.11.6
18:15
Authors : Ricardo Brandolt, Ricardo Paupitz
Affiliations : Sao Paulo State University (UNESP)

Resume : Collision dynamics of highly accelerated fullerenes on two important 2-dimensional materials, namely the graphenylene and the porous graphene, was theoretically investigated. These materials have been considered as candidates for the construction of molecular sieves and possible applications in nanoelectronics in the near future. Our calculations were carried using Molecular Dynamics methods while inter-atomic interactions were described by the ReaxFF reactive potential. Our results indicate that there are several different behaviors which are highly dependent on the incident angle, projectile velocity and the material being considered. Graphenylene and Porous graphene behavior under the action of the projectile are compared to similar simulations we have done for graphene in the same conditions (same incident angles and velocities) and with results found in the literature for massive projectiles on graphene. We conclude that the 2d materials investigated in our study present behaviors which are both different from what happens with graphene and exhibit some new features. Also, the several regimes observed were mapped in a diagram for each one of the considered membranes.

AA.11.7
18:30
Authors : Yicun Huang, Sarah L. Masters, Susan P. Krumdieck, Catherine M. Bishop
Affiliations : Department of Mechanical Engineering, University of Canterbury; School of Physical and Chemical Sciences, University of Canterbury; Department of Mechanical Engineering, University of Canterbury; Department of Mechanical Engineering, University of Canterbury;

Resume : Controlling the interfaces, including the free surfaces, of thin films is of crucial importance for photo-catalysis applications. A novel, polycrystalline, titania film grown by chemical vapour deposition possesses unusual anatase dendrites with plate-like secondary features and has demonstrated excellent photocatalytic and antimicrobial activity. The activity is thought to be related to the crystallography of the exposed surfaces and nanostructure. The unusual microstructure is hypothesised to result from the interplay between shadowing due to ballistic deposition at low pressures and highly anisotropic surface diffusion. There is no existing modelling framework to facilitate the study of interrelations of these two effects. In this work, we focus on the formation of the kinetically frozen facets and employ a phase-field model to incorporate both process-specific and materials-specific effects. The surface morphology and crystallography at various stages of film growth and analysis of surface roughening exponents can be obtained, and will be compared to experimental results. The modelling and analysis here will enable engineering of film growth conditions to obtain optimal performance of these titania films. It will provide insight into the controlling processes that result in active surfaces. This novel modelling approach can be extended to other thin film vapour growth processes.

AA.11.8
19:00 Graduate Student Award ceremony followed by the social event    
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Materials by design 2 : -
08:30
Authors : Fumiyasu Oba
Affiliations : MSL-IIR & MCES, Tokyo Institute of Technology, Japan; CMI2, MaDIS, National Institute for Materials Science, Japan

Resume : The search for novel semiconductors is increasingly important as the applications of semiconductors become more prevalent in modern society. This situation stimulates not only experimental but also computational exploration of as-yet-unreported semiconductors, typically using first-principles calculations. In such computational searches, reliable design principles, as well as accurate and efficient computational schemes, are key requirements for successful identification of target materials and functionalities. In this talk, I will discuss the design and exploration of semiconductors using first-principles calculations. Topics to be covered include the prediction of a novel nitride semiconductor CaZn2N2 [1] and p-type Cu3N via chemical doping of F [2], both of which have been verified experimentally, as well as computational methods for the prediction of fundamental and defect properties of semiconductors [3]. [1] Y. Hinuma, T. Hatakeyama, Y. Kumagai, L. A. Burton, H. Sato, Y. Muraba, S. Iimura, H. Hiramatsu, I. Tanaka, H. Hosono, and F. Oba, Nat. Commun. 7, 11962 (2016). [2] K. Matsuzaki, K. Harada, Y. Kumagai, S. Koshiya, K. Kimoto, S. Ueda, M. Sasase, A. Maeda, T. Susaki, M. Kitano, F. Oba, and H. Hosono, Adv. Mater. 30, 1801968 (2018). [3] F. Oba and Y. Kumagai, Appl. Phys. Express 11, 060101 (2018).

AA.12.1
09:00
Authors : Thomas A. A. Batchelor, Jack K. Pedersen, Simon J. Winther, Ivano E. Castelli, Karsten W. Jacobsen, Jan Rossmeisl
Affiliations : T. Batchelor - Department of Chemistry, University of Copenhagen; J. Pedersen - Department of Chemistry, University of Copenhagen; S. Winther - Department of Chemistry, University of Copenhagen; I, Castelli - Department of Energy Conversion and Storage, Technical University of Denmark; K. Jacobsen - Department of Physics, Technical University of Denmark; J. Rossmeisl - Department of Chemistry, University of Copenhagen

Resume : High-entropy alloys (HEAs) provide a near-continuous distribution of adsorption energies. This can increase overall catalytic activity since a minority of binding sites have optimal properties for catalysis, even though the majority of sites are ineffectual. In this report we focus on the oxygen reduction reaction (ORR), where we present the results of DFT calculated *OH and *O adsorption energies on a random subset of the available binding sites on the surface of HEA IrPdPtRhRu. A simple machine learning algorithm was used to predict the remaining distribution of adsorption energies. We found very good agreement between DFT calculated and predicted values. With a full catalog of available binding sites and corresponding adsorption energies an appropriate expression for predicting catalytic activity was used to optimise the HEA composition by maximising the probability of finding optimal sites. The HEA then becomes a design platform for the unbiased discovery of new alloys by focusing on these sites with exceptional catalytic activity. Setting different optimisation constraints led to a new HEA composition and a binary alloy IrPt, demonstrating significant enhancements over pure Pt(111).

AA.12.2
09:15
Authors : Felix Tim Bölle , August Edwards Guldberg Mikkelsen, Tejs Vegge, Ivano E. Castelli
Affiliations : Felix Tim Bölle - Atomic Scale Materials Modelling, Department of Energy Conversion and Storage, Technical University of Denmark; August Edwards Guldberg Mikkelsen - Atomic Scale Materials Modelling, Department of Energy Conversion and Storage, Technical University of Denmark; Tejs Vegge - Atomic Scale Materials Modelling, Department of Energy Conversion and Storage, Technical University of Denmark; Ivano E. Castelli - Atomic Scale Materials Modelling, Department of Energy Conversion and Storage, Technical University of Denmark;

Resume : Reducing dimensionality has led to a new realm of materials exhibiting interesting structural, electronic and catalytic properties. While two dimensional materials are the focus of many theoretical and experimental research groups, one dimensional materials are less well studied. Most of the theoretical work on 1D materials is focused on explaining phenomena at the atomic-scale rather than performing a high-throughput search of new inorganic nanotube materials. Here, we investigate by means of density functional theory (DFT) sub-nanometer tubes that exhibit different properties compared to their 2D counterparts while being selective in size and composition. Sub-nanometer tubes have the advantage of tunable properties as well as fewer atoms in the unit cell making them suitable for DFT calculations. The phase space of the ternary, three layered materials comprises various metals plus a combination of group 6 and 7 elements. We will elucidate designing rules to produce nanotubes with controlled dimensions. Additionally, data-driven design rules guide the search towards nanotubes that can be used in a variety of applications. In detail we focus on properties like bandgaps, stabilities and adsorption energies that lead to predictive models assisting in designing new nanotubes before doing DFT calculations. The generalization from existing data helps to accelerate the search for novel materials for applications in batteries, (photo-)catalysis,chemical storage and nanofluidics.

AA.12.3
09:30 Coffee break    
 
Materials by design 3 : -
10:00
Authors : Andriy Zakutayev
Affiliations : National Renewable Energy Laboratory

Resume : Materials discovery is one of the most important directions in materials research, as new materials often enable new technologies. Some materials chemistries, such as oxides, have been extensively explored in the past, and yielded many spectacular properties including high-temperature superconductivity, piezo/ferro-electricity, and transparent conductivity. Other subfields of the broad materials space, such as nitrides, have been barely touched: for every 14 documented oxides there is only 1 known nitride [1]. In this talk, I will present on data-driven and computations-fueled experimental synthesis and characterization of new nitride materials. Recent calculations indicated that there are 92 uncharted ternary metal nitride chemical spaces and 213 stable ternary materials with specific structures predicted from first principles [2] Experimental synthesis using high-throughput combinatorial methods realized 7 of these 92 compounds, including the Mg-TM-N family, where M = Nb, Ti, Zr, Hf in the rocksalt-derived crystal structure. Physical property characterization results indicate that these ternary nitrides are semiconductors with 1.8-2.1 eV optical absorption onsets and large dielectric constants [3]. One of these materials, MrZrN2 shows composition-tunable electrical conductivity and electron mobility up to 100 cm2/Vs when grown on MgO substrate. Overall, these results support the usefulness of the computational screening for discovery of new materials, and suggest that many new previously unreported nitride materials remain to be synthesized. The large amount of data resulting from these and other combinatorial experiments at NREL are incorporated into the High Throughput Experimental Materials” database (HTEM DB) available at https://htem.nrel.gov/, and can be used in conjunction with computational property databases for data mining and machine learning purposes. [1] J. Mater. Chem. A 4, 6742 (2016) [2] arXiv:1809.09202 [3] arXiv:1810.05668 [4] Scientific data, 5, 180053 (2018)

AA.13.1
10:30
Authors : Joseph R. Nelson; Chris J. Pickard
Affiliations : Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom; Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan

Resume : The physical properties of a material are tightly related to its crystal structure, and predicting the former is usually impossible without knowledge of the latter. The last decade and a half has seen the emergence of several computational methods that allow crystal structure to be predicted from first principles. In this talk, we discuss ab initio random structure searching (AIRSS), a simple yet powerful tool for predicting crystal structure. AIRSS relies on the local relaxation of randomly-generated sensible candidate structures, which incorporate reasonable constraints (such as crystal symmetry) where available [1-3]. We showcase several applications of the method, focusing on high-pressure superconducting hydrogen sulfide [4], and on predicting materials for lithium and sodium ion battery anodes [5], where AIRSS is used alongside data mining approaches. Finally, we briefly describe the recently introduced geometry optimisation of structures from hyperspace method (GOSH) [6]. GOSH extends traditional structural optimisation into higher dimensions, and we show how this can dramatically improve random search methods like AIRSS. [1] C. J. Pickard and R. J. Needs, Phys. Rev. Lett. 97, 045504 (2006). [2] C. J. Pickard and R. J. Needs, J. Phys.: Condens. Matter 23, 053201 (2011). [3] AIRSS code v0.9.1; available at https://www.mtg.msm.cam.ac.uk/Codes/AIRSS [4] Y. Li, L. Wang, H. Liu, Y. Zhang, J. Hao, C. J. Pickard, J. R. Nelson, R. J. Needs, W. Li, Y. Huang, I. Errea, M. Calandra, F. Mauri, and Y. Ma, Phys. Rev. B 93, 020103(R) (2016). [5] L. E. Marbella, M. L. Evans, M. F. Groh, J. R. Nelson, K. J. Griffith, A. J. Morris, and C. P. Grey, J. Am. Chem. Soc. 140, 7994-8004 (2018). [6] C. J. Pickard, accepted in Phys. Rev. B (2019).

AA.13.2
10:45
Authors : Catherine M. Bishop, Oscar A. Torres-Matheus, R. Edwin Garcia
Affiliations : Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch, 8140, New Zealand; Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch, 8140, New Zealand; School of Materials Engineering, Purdue University, Neil Armstrong Hall of Engineering 701 West Stadium Avenue, West Lafayette, IN 47907, USA

Resume : Lead toxicity has motivated the search for Pb-free ferroelectrics to replace PZT, whose optimal properties near its interferroelectric transition are associated with a reduction of the crystallographic anisotropy of the free energy. Existing modelling methodologies artificially couple the free energies of the bulk ferroelectric phases with different symmetries found near a transition. Thus, the interferroelectric transition and structural states in ceramics near this region of phase space are not able to be examined. Here a novel phase-field approach is proposed to describe PPB ferroelectrics, with a temperature induced transition. The formulation allows the properties of the two ferroelectric phases to vary independently. Model parameters are fitted to experimental data from BZT-40BCT ceramics. There is debate about whether this system has a single PPB with a region of rhombohedral tetragonal (R T) coexistence or whether there is an intervening orthorhombic (O) phase. Our predictions for BZT-40BCT are consistent with experimental observations of an R T coexistence region. A maximum temperature for coexistence is predicted from thermodynamic analysis and agrees with the experimentally observed upper transition temperature. The time-temperature-transformation behaviour indicates that low temperature coexistence is kinetically limited. This method can be used to validate competing theories regarding the enhanced properties near the PPB in the search for Pb-free materials.

AA.13.3
11:15 PLENARY SESSION 2    
12:30 Lunch    
 
Battery materials 1 : -
13:45
Authors : Pieremanuele Canepa(a)
Affiliations : (a) Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore

Resume : Batteries that replace Li+ ions with inexpensive multivalent (MV) cations, including Mg2+, Zn2+ and Ca2+ represent a promising approach to meet the high energy density requirements of the next generation of electrical devices.[1] Perhaps the most pressing challenge in achieving high energy density MV-ion systems is to develop suitable cathode materials and conductors with a significant voltage and high MV-ion transport.[1-2] To date, there have been limited examples demonstrating the feasibility of rechargeable MV batteries, and among them, most of the focus has been on Mg technology. From the limited experimental studies performed so far, the feasibility of a battery technology based on MV intercalation is not yet clear. The cathode represents a critical component of this technology. Therefore, it is crucial to assess the feasibility of MV cathodes. I will present a detailed analysis, based on first-principles DFT calculations, of MV intercalation in promising candidates, including the spinel MVB2X4 system (with B = transition metal and X the anion) and the polymorphs of the layered vanadium pentoxide (V2O5).[1-7] I will demonstrate that computational materials science is a powerful tool to pave the successful development and optimization of new materials for energy dense MV batteries. References: [1] P. Canepa, G. S. Gautam, D. C. Hannah, R. Malik, M. Liu, K. G. Gallagher, K. Persson and G. Ceder, Odyssey of Multivalent Cathode Materials: Open Questions and Future Challenges, Chem. Rev., 2017, 117 (5), 4287. [2] P. Canepa, S.-H. Bo, G. S. Gautam, B. Key, W. D. Richards, T. Shi, Y. Tian, Y. Wang, J. Li and G. Ceder, High magnesium mobility in ternary spinel chalcogenides, Nature Communications, (2017) 8, 1759. [3] G. S. Gautam, P. Canepa, R. Malik, M. Liu, K. Persson and G. Ceder, First-principles evaluation of multi-valent cation insertion into orthorhombic V2O5 [4] Z. Rong, R. Malik, P. Canepa, G. S. Gautam, M. Liu, A. Jain, K. Persson and G. Ceder, Materials Design Rules for Multi-Valent Ion Mobility in Intercalation Structures, Chem. Mat. 2015, 27, 6016. [5] M. Liu, Z. Rong, R. Malik, P. Canepa, A. Jain, G. Ceder and K. Persson, Spinel compounds as multivalent battery cathodes: a systematic evaluation based on ab initio calculations, Energy Environ. Sci. 2015 8, 964. [6] G. S. Gautam, P. Canepa, A. Abdellahi, A. Urban, R. Malik and G. Ceder, Intercalation phase diagram of Mg in V2O5 from first principles, Chem. Mat. 2015, 27, 3733. [7] M. Liu, A. Jain, Z. Rong, X. Qu, P. Canepa, R. Malik, K. Persson and G. Ceder, Evaluation of sulfur spinel compounds for multivalent battery cathode applications, Energy Environ. Sci., 2016, 9, 3201.

AA.14.1
14:15
Authors : Julia Savioli, Graeme W. Watson
Affiliations : School of Chemistry and CRANN, Trinity College Dublin

Resume : Solid oxide fuel cells (SOFC) directly convert chemical energy into electrical power in an environmentally friendly way and have been widely studied as an alternative to fossil fuel-based technologies. Extensive research has been made to develop electrolyte materials with high ionic conductivities in the intermediate temperature (IT) range (873-1073 K), since the high temperatures (1073-1300 K) currently required for SOFC operation decrease the life-time of the device. Aliovalent doping of LaGaO3 generates oxygen vacancies and enhance the perovskite oxide-ion conductivity, enabling its application as solid electrolyte in IT-SOFCs. This process can be favored by changes in the concentration and “identity” of dopants, which interact with the oxygen vacancies, affecting their mobility and the ionic transport properties of the material. DFT calculations using the meta-GGA SCAN functional were performed to investigate the effects of a series of divalent metals as dopants in LaGaO3 and their influence in the defect chemistry and ionic conductivity of the perovskite. Key features that impact the ionic conductivity – the doping energy, the preferable doping site (La or Ga site) and the association energy between vacancies and dopants – were investigated as a function of dopant identity and chemical environment. The behavior of the oxygen vacancies was determined to be associated with the ionic radii and electronic structure of the considered dopants.

AA.14.2
14:30
Authors : Adam McSloy 1, Peter R. Slater 2, Paul Kelly 1, Pooja M. Panchmatia*1
Affiliations : 1 Department of Chemistry, Loughborough University, Loughborough LE11 3TU, UK 2 School of Chemsitry, University of Birmingham, Birmingham B15 2TT, UK

Resume : Recently, A2BO4 type materials have been the focus of recent research as the search for new fast ion conductors, electro-ceramics and carbon capture materials has become more important than ever before. One such material, barium orthotitanate (Ba2TiO4), is unusual in that it is one of the few examples of tetrahedrally coordinated Ti4+ ions..[1] However, this material is both hygroscopic and highly reactive towards carbon dioxide – characteristic which may inhibit fast oxide ion conduction. In this work, atomic scale modelling techniques have been employed to investigate water and carbon dioxide incorporation in Ba2TiO4, and to interrogate the resulting defect structures formed. Such methods of investigation offer an insight into defects which is difficult to attain through experimental means. Our investigations have revealed that carbonate impurities are likely to be common in both pristine and doped Ba2TiO4 systems alike. Whereas those based on water will likely only form when oxygen vacancies or interstitials are present. However, both impurities are likely to trap oxide ion defects if present. References [1] Y. Saito, Y. Sakabe, Fuel Cell, 5. (2005) 5–8.

AA.14.3
14:45
Authors : Dr. Ivana Radosavljevic Evans, Dr. Joseph Peet, Dr. Andrea Piovano, Prof. Mark Johnson
Affiliations : Department of Chemistry Durham University Durham DH1 3LE UK Institut Laue Langevin 71 Avenue des Martyrs 38000 Grenoble France

Resume : An in-depth understanding of the composition - structure – property relationships is essential for the successful discovery and preparation of new functional materials capable of overcoming the limitations of the ones currently used in applications. As materials’ complexity increases, characterisation using a range of experimental techniques (e.g. diffraction/scattering-based techniques and complementary property measurements), as well as state-of-the-art data analysis approaches and computational simulations, is essential in providing this insight. This presentation will give an overview of our recent work on oxide ion conductors for energy applications: the elucidation of the key design principles, defects and mechanisms giving rise to ionic mobility; the development and use of advanced structural data analysis methodologies capable of tackling exceptionally complex crystallographic problems arising from phase transitions; the complementary use of long-range and local structural probes in understanding the structure, properties and disorder. [1] M. L. Tate, D. A. Blom, M. Avdeev, H. E. A. Brand, G. J. McIntyre, T. Vogt and I. Radosavljevic Evans, Advanced Functional Materials, 27, 8, 1605625 (2017). [2] J. R. Peet, C. A. Fuller, B. Frick, M. Zbiri, M. R. Johnson and I. Radosavljevic Evans., Chemistry of Materials, 429, 7, 3020 (2017). [3] J. R. Peet, A. Piovano, M. R. Johnson and I. Radosavljevic Evans., Dalton Transactions, 46, 15996 (2017). [4] J. R. Peet, M. R. Chambers, A. Piovano, M. R. Johnson and I. Radosavljevic Evans., Journal of Materials Chemistry A, 6, 12, 5129 (2018).

AA.14.4
15:00
Authors : Elif Ertekin
Affiliations : Department of Mechanical Science and Engineering and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana IL 61801, USA

Resume : Materials for electrochemical device components such as fuel and electrolysis cell electrodes often require large, tunable ionic and electronic conductivity. The design and optimization of such materials remains a longstanding challenge, in part due to the chemical space complexity. Materials that exhibit mixed ionic and electronic conductivity (MIECs) tend to be disordered mixtures whose composition and stoichiometry are sensitive to the thermodynamic environment. In this presentation, I will describe our recently proposed approach to predicting the ionic and electronic conductivity of disordered perovskite oxide mixtures exhibiting large partial substitutions on the perovskite sublattices AA'BB'O3-x. Our approach relies on (i) first-principles to establish defect equilibria and predict of stoichiometry and oxygen content under different thermodynamic environments and (ii) a green's function method to prediction of the oxygen ion diffusion coefficients for disordered configurations at different compositions. We demonstrate the method for the classic perovskite oxide MIEC Sr(Ti1-xFex)O3-y across the full composition space 0 < x < 1, and show that the Sr-Ti-Fe-O composition space can be well-described as a solid solution between the band insulator SrTiO3 and the ordered oxygen vacancy compound Sr2Fe2O5 under a wide variety of temperatures and oxygen partial pressures. The predicted compositions Sr(Ti1-xFex)O3-x/2+d deviate from the reference composition d = 0 under oxidizing or reducing environments, resulting in p-type or n-type carrier concentrations for d > 0 or d < 0 respectively. The predicted stoichiometries and carrier concentrations are in good agreement with experiment. To predict ionic diffusivity, a cluster expansion model is used to predict configuration energies and cluster expansion Monte Carlo simulations are used to predict representative alloy configurations under different temperatures and gas environments. The diffusivity tensor is obtained from site and transition state energies as steady-state solutions to the diffusion master equation. This represents a scalable approach to capturing properties such as diffusivity in complex disordered alloy materials. We will also show preliminary results of this application of this framework to the Sr-Ti-Co-O and La-Sr-Co-O perovskite oxide phase space.

AA.14.5
15:30
Authors : Anastassia Sorkin, Haomin Chen, Stefan Adams
Affiliations : Department of Materials Science and Engineering, National University of Singapore

Resume : Safety hazards and unsatisfactory cost-performance ratio have become key bottlenecks for a wider market penetration of batteries. Trial-and-error based evolution of battery technologies is too slow to fully make use of opportunities in the “materials genome” for developing safer, higher performance and lower cost batteries. Artificial intelligence systems can help by providing unbiased predictions of more promising systems on a rational basis with less prejudice towards devices “in the comfort zone” of research groups. Ab initio calculation methods could provide accurate data for this rational design, but are too slow and size-limited to cover the genome of complex battery materials. Empirical potentials such as our “softBV” parameter set enable high throughput calculations at the expense of reduced reliability as they are derived from parameters fitted to experimental reference data sets that may contain experimental errors. Plausibility checks and iterative optmisation of the reference crystal structures are thus a crucial part of the effort. The key step is to move on from modelling individual materials to simulating electrode|electrolyte combinations and their interfaces and relate them to experimental characterization of these devices during cycling by operando techniques (solid state NMR, Raman, XRD, electrochemical characterization, mechanical testing). This allows to deal both with the electrochemical stability of the interface as well as the often hardly understood charge transfer impedances that are crucial for device performance.

AA.14.6
15:45
Authors : Lushi Cheng
Affiliations : Supervisors: Dr Clotilde Cucinotta and Prof. Nicholas Harrison

Resume : Magnesium (Mg) and its alloys are promising materials to be used in automotive and aerospace due to the light-weight property of Mg. However, the high corrosion rate of Mg in aqueous environment limits its use in engineering applications, maybe because of the negative difference effect (NDE) of Mg. In the initial stages of Mg corrosion, after Mg2+ dissolves into solution, with the accumulation of electrons in the bulk of Mg, the anodic potential is increased and the cathodic hydrogen gas (H2) generation should decrease. However, when the anodic potential is further increased, it has been observed that the rate of hydrogen revolution is actually increased. One of the hypothesises accounting for this unusual phenomenon is the existence of Mg+ as an intermediate before transforming into Mg2+, and Mg+ reacts with water to produce extra H2. To examine this hypothesis, first principles DFT (density functional theory) methods and CP2K code will be used to model Mg corrosion by first investigating the properties, bonding relationships, density of states, potential and charge density of bulk of Mg and its surface. Then, water multilayers will be added on Mg surface to study the Mg-water interactions, followed by thermodynamic calculations of Mg to Mg+, Mg+ to Mg2+ and Mg to Mg2+ in both vacuum and aqueous environment.

AA.14.7
16:00 Coffee break    
 
Battery materials 2 : -
16:30
Authors : Ranjini Sarkar, T.K. Kundu
Affiliations : Indian Institute of Technology Kharagpur; Indian Institute of Technology Kharagpur

Resume : Electro-active polymer β-polyvinylidene fluoride (β-PVDF) based ferroelectric composites have gained significant technological importance over conventional ceramic ferroelectrics. But synthesis of β-PVDF has been a challenge owing to its structural instability. Hydrated metal salt systems are found as one of the additive materials which effectively induce polar β-PVDF from non-polar PVDF blend (which contains majorly α phase). This article provides quantum chemical description of PVDF – hydrated aluminium nitrate salt composite system in the light of density functional theory. Four monomer units of pristine α and β-PVDF, pure Al(NO3)3.9H2O, and PVDF/ Al(NO3)3.9H2O structures are optimized using dispersion corrected exchange correlation functional B3LYP-D3 and 6-311+G(d,p) basis set. Similar to the experimental findings, the current theoretical investigation also suggests that hydrogen bond interaction between PVDF and the hydrated salt molecule plays the major role for the enhancement of ferroelectric properties in this composite system. Non-covalent interaction phenomenon is elucidated in detail on the basis of natural bond orbital analysis, Bader’s quantum theory of atoms in molecules and reduced density gradient analysis. Chemical reactivity and charge transfer mechanisms are explained using molecular electrostatic potential plot, frontier molecular orbital analysis and atomic-dipole corrected Hirshfeld population analysis, respectively.

AA.15.1
16:45
Authors : Gabriele Saleh, Stefano Sanvito, Chen Xu
Affiliations : Istituto Italiano di Tecnologia, Via Morego 30, Genova, Italy; School of Physics, AMBER and CRANN institute, Trinity College Dublin, College Green, Dublin 2, Ireland; Nokia Bell Labs, 600 Mountain Avenue, Murray Hill, NJ, USA

Resume : Silver is broadly adopted in electronics, although its tendency to degrade by reacting with the environment (Ag tarnishing) represents a severe limitation. Ag is easily tarnished by sulphur compounds, even at ppb concentrations, but hardly reacts with O2, despite thermodynamics predicts both sulphide and oxide to form favorably at ambient conditions[1]. In fact, the formation enthalpies of Ag2S and Ag2O are almost identical[1]. The reactivity disparity is thus to be sought in the reaction dynamics, that is the focus of this contribution. We performed extensive Molecular Dynamics (MD) simulations of Ag/S and Ag/O reactions by employing reactive force fields (ReaxFF [2]). We unearthed the different mechanisms of silver oxidation and sulphidation, thereby explaining why the latter but not the former takes place. The influence of various defects on Ag reactivity is also considered. Ab initio calculations are performed to confirm and further rationalize the MD findings. Additionally, our results recover (and explain) a number of experimental results from literature. Importantly, for this study we developed new ReaxFF force fields and a protocol to test them extensively against ab initio results. We demonstrate that the procedure generally adopted in literature to generate ReaxFF force fields does not guarantee a sufficient accuracy for the molecular dynamics simulation. [1] P. Patnaik “Handbook of Inorganic Chemicals” [2] A.C.T. van Duin et al., J. Phys. Chem. A 105, 9396 (2001)

AA.15.3
17:00
Authors : Sebastian Siol (1), Aaron Holder (2,3), Stephan Lany (2), Andriy Zakutayev (2)
Affiliations : (1) EMPA, Swiss Federal Laboratories for Science and Technology, CH-8600 Dübendorf, Switzerland (2) National Renewable Energy Laboratory, Golden, Colorado 80401, United States (3) University of Colorado, Boulder, Colorado 80309, United States

Resume : The stabilization of high-energy polymorphs is considered a key challenge in materials design and discovery. High-energy polymorphs with unusual properties are routinely synthesized by compression under positive pressure. However, changing a material’s structure by applying tension under negative pressure is much more difficult. Here we show how negative-pressure polymorphs can be synthesized by mixing materials with different crystal structures—a general approach that is applicable to many materials. Theoretical calculations suggest that it costs less energy to mix low-density structures than high-density structures, due to less competition for space between the atoms. Proof-of-concept experiments confirm that mixing two different high-density forms of MnSe and MnTe stabilizes a Mn(Se,Te) alloy with a low-density wurtzite structure. This Mn(Se,Te) polymorph shows up to 4× lower electron effective mass compared to its MnSe and MnTe parent compounds and a piezoelectric response that none of the parent compounds have [1]. We show how this design principle can be applied to other material combinations which show a suitable ordering of the endmember polymorph energies [2]. Finally, we discuss how this conceptual approach can be used to screen high-throughput computational databases, potentially revealing numerous material systems where such novel metastable polymorphs can be discovered. 1. S.Siol et al. Sci.Adv. 4, eaaq1442, 2018 2. Y.Han et al. J.Phys.Chem.C 122, 18769–18775, 2018

AA.15.4
17:15
Authors : Janis Timoshenko, Mahdi Ahmadi, Farzad Behafarid, Beatriz Roldan Cuenya
Affiliations : Department of Interface Science, Fritz-Haber-Institute of the Max Planck Society, 14195 Berlin, Germany; Department of Physics, University of Central Florida, Orlando, FL 32816, USA; Department of Physics, University of Central Florida, Orlando, FL 32816, USA; Department of Interface Science, Fritz-Haber-Institute of the Max Planck Society, 14195 Berlin, Germany and Department of Physics, University of Central Florida, Orlando, FL 32816, USA

Resume : Despite the significant progress in experimental tools for nanoparticle (NP) characterization and theoretical NP modeling approaches, understanding of the relation between intriguing properties of metal NPs (e.g., catalytic activity or unique thermodynamic characteristics) and their structure is a challenging task. The intrinsic complexity and heterogeneity of NPs, their interactions with the support, ligands and adsorbates, strong static disorder and anharmonic effects at NPs surface, or in situ transformations of their structure pose significant difficulties both for theoretical modeling and for the interpretation of experimental data. We address this problem by bridging theoretical modeling (molecular dynamics (MD)) and experimental approaches (extended X-ray absorption fine structure spectroscopy (EXAFS)) via machine learning methods. We use simple MD models to train an artificial neural network (NN) to establish the relationship between EXAFS features and NPs structural characteristics, and subsequently to guide the interpretation of experimental data in a real system. Here we employ this method to follow the structural evolution of SiO2-supported Pt NPs upon temperature increase. NN-EXAFS analysis and a unique configuration of our experiment (size-selected, adsorbate- and ligand-free NPs in UHV) allow us to shed new light on a controversial phenomenon such as negative thermal expansion, which has been previously reported for small supported metal NPs.

AA.15.5
17:30
Authors : Daniel Fritsch (1), Susan Schorr (1,2)
Affiliations : (1) Department Structure and Dynamics of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany; (2) Department of Geosciences, Freie Universität Berlin, Malteserstr. 74-100, 12249 Berlin, Germany

Resume : In recent years, kesterite-type compound semiconductors such as Cu2ZnSnS4 and Cu2ZnSnSe4 (CZTSSe) received a lot of attention due to their possible application as absorber layers in low-cost thin-film solar cells. However, substituting Ge4+ for Sn4+ in CZTSSe kesterite-type absorber layers has been shown to enhance the band gap and improve the optoelectronic properties [1]. Here, we address the computational modelling of intrinsic vacancy defects, antisite defects, and intrinsic point defects in kesterite-type Cu2ZnGeSe4. The calculations employ density functional theory together with the PBEsol and the more accurate hybrid functional HSE06. Details of the intrinsic defects’ characteristics will be discussed, as well as their influence on the electronic and optical properties. This work made use of computational resources provided by the North-German Supercomputing Alliance (HLRN), and the Soroban and Dirac HPC facilities of the Freie Universität Berlin and the Helmholtz-Zentrum Berlin, respectively. [1] R. Gunder, J. A. Márquez-Prieto, G. Gurieva, T. Unold, and S. Schorr, Cryst. Eng. Comm. 20, 1491 (2018).

AA.15.6
17:45
Authors : Claire Tjokrowidjaja
Affiliations : Professor Nicholas Harrison; Professor Sandrine Heutz

Resume : A high temperature molecular magnet could be used to replace current applications of metal-based systems. Additionally, it would have all the benefits of synthetic chemistry and could be grown as a thin film. In combination with semiconducting properties, this would allow it to be used in spintronic applications. Only one molecule has been reported to consistently achieve room temperature magnetism: the V[TCNE]x system. However, its thin film growth is challenging. Other molecules which have been routinely integrated into optoelectronic devices have been shown to exhibit magnetism, notably cobalt phthalocyanine (CoPc) which has shown magnetic ordering up above 100 K in its alpha phase. Here computational chemistry is used to probe potential systems based on phthalocyanine. In CoPc and other metal phthalocyanine systems, theoretical work has shown that magnetic ordering increases with stacking angle. Different strategies such as changing the metal centre, using combinations of different metals and investigating non-planar systems have been implemented to increase the exchange energy.

AA.15.7
18:00
Authors : 1. P. Palacios, 2. G. García, 2. P. Sanchez-Palencia, 3. J.E. Castellanos, 4. A. Montero-Alejo, 4. E. Menéndez-Proupin, 5. J. C. Conesa, 2. P. Wahnón
Affiliations : 1. Instituto de Energía Solar and Dept. FAIAN, E.T.S.I. Aeronáutica y del Espacio, Universidad Politécnica de Madrid, Spain; 2. Instituto de Energía Solar and Dept. TFB, E.T.S.I. Telecomunicación, Universidad Politécnica de Madrid, Spain; 3. Universidad de Guanajuato, Dept. Estudios Multidisciplinarios, Yacatitas, Yuriria, Gto. C.P. 36940 México. 4. Departamento de Física, Facultad de Ciencias, Universidad de Chile, Santiago, Chile 5. Instituto de Catálisis y Petroleoquímica, CSIC, Marie Curie 2, 28049 Madrid, Spain.

Resume : We present in this work several materials actively studied as good absorbers for photovoltaic applications. These materials have been proposed to boost photovoltaic efficiency through coupling the absorption of two low energy photons to achieve a higher energy electron excitation. We have verified earlier with accurate density functional theory (DFT) calculations and beyond (HSE, GW), that semiconductors as chalcopyrite CuGaS2, spinel In2S3 or layered SnS2 can provide this situation when a cation in their structure is partially substituted by an element such as transition metal. New studies on doped InP and SnS2 will be presented here. Experimental works verify that new absorption features appear in the optical absorption spectrum which matches the predicted DFT-based and more advanced theoretical absorption results. We report also the investigation of the electronic structure of doped perovskites (CH3NH3PbI3). The study suggests that the presence of point defects play an important role in the coupling of two low energy photons to achieve a higher energy electron excitation, which would maximize the photovoltaic performance.

AA.15.8
18:15
Authors : Giulia Biffi, Francesco Segatta, Vincenzo Caligiuri, Marco Garavelli, Roman Krahne,Ivan Rivalta
Affiliations : Istituto Italiano di Tecnologia, Optoelectronics,Genova, Italy - Università degli Studi di Bologna, Dipartimento di Chimica Industriale “Toso Montanari”, Bologna, Italy - Università degli Studi di Genova, Dipartimento di Chimica e Chimica Industriale, Genova, Italy ; Università degli Studi di Bologna, Dipartimento di Chimica Industriale “Toso Montanari”, Bologna, Italy ; Istituto Italiano di Tecnologia, Optoelectronics,Genova, Italy ; Università degli Studi di Bologna, Dipartimento di Chimica Industriale “Toso Montanari”, Bologna, Italy ; Istituto Italiano di Tecnologia, Optoelectronics,Genova, Italy ; Università degli Studi di Bologna, Dipartimento di Chimica Industriale “Toso Montanari”, Bologna, Italy - Université de Lyon, École Normale Supérieure de Lyon, CNRS, Université Claude Bernard Lyon 1, Laboratoire de Chimie UMR 5182, F-69342, Lyon, France

Resume : Push-pull chromophores have gained interest as their nanocrystals display aggregation-induced fluorescence and two-photon absorption. Due to their customizability[1], these nanoparticles proved themselves promising for applications in optics and in nanomedicine as selective high-resolution biosensors[2],[3]. To design push-pull chromophores withspecific optical response (high brightness, high refractive index, large Stokes’ shift) demanding theoretical and computational efforts are required. Our modeling strategy involved single molecule ab initio studies followed by simulations based on a “supermolecular” approach and using various levels of approximation for modeling the excitons in the extended material. Here, we demonstrate that combining ab initio computations with Frenkel excitonic models it is possible to reproduce the main spectroscopic features of nanocrystals of an organic push-pull chromophore. Moreover, we simulated the refractive index of this molecule and compared with experimental studies based ellipsometric measurements. The outcome showed surprisingly high refractive index, with potential applications in the field of metamaterials. [1]J. Oudar, J. Chem. Phys. , pp. 446-457, 1977 [2]S.M.A. Fateminia et al., Adv. Mat. , p. 1604100, 2017 [3]S.M.A. Fateminia et al., Small Methods, p. 1600023, 2017

AA.15.9

No abstract for this day


Symposium organizers
Ivano CASTELLITechnical University of Denmark

Department of Energy Conversion and Storage, Fysikvej 309, DK-2800 Kgs. Lyngby, Denmark

+45 53538491
ivca@dtu.dk
Vladan STEVANOVICColorado School of Mines

1500 Illinois St., Golden, CO 80401, USA

+1 720 236 3534
vstevano@mines.edu