Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J28: Focus Session: Computational Materials Design - Data-Driven |
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Sponsoring Units: DCOMP DMP Chair: Long-Qing Chen, Penn State University Room: C156 |
Tuesday, March 22, 2011 11:15AM - 11:51AM |
J28.00001: Distributed Strategies for Materials Development Invited Speaker: Through appropriate combinations of ``ab-initio,'' ``data-mining-high-throughput,'' ``cluster expansion,'' ``vibrational,'' and ``electronic structure'' techniques, we have parameterized the whole set of transition-metal binary intermetallics (435 alloys) and a list of $\sim$10,000 inorganic crystals. The presentation will introduce the method, the tools, the standards, and the approach for automatic discovery of trends in material development. We will analyze rules for miscibility in metallic catalytic materials, electronic structure correlations in scintillators, and high-throughput search of thermoelectric materials and topological insulator through the distributed network of data, accessible to the scientific community. The presentation will also extend the hybrid method to study phenomena at the nanoscale, like size-induced viscosity effects on the catalytic rate, self-consistent variational approaches to the shape of nano-catalysts and size-dependent Wulff plots for tailoring catalysts compositions and size (Sponsors: ONR, NSF, DHS, Teragrid). [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:03PM |
J28.00002: A database survey to search for new candidate {\em p}-type TCOs Giancarlo Trimarchi, K. Poeppelmeier, A. J. Freeman New {\em p}-type TCOs are often produced by reacting the prototype binary {\em p}-type oxides, i.e., Ag$_{2}$O and Cu$_{2}$O, with binary oxides of other transition metals or main-series elements. Yet, so far only a small part of all the multi-cation Cu and, in particular, Ag oxides have been assessed as candidate {\em p}-type TCOs. Furthermore, numerous multi-species Cu and Ag oxide systems are poorly characterized, which leaves ample scope for discovery of yet unknown compounds belonging to them, and, likely, of unsuspected new TCOs, too. Here, we survey a {\em complete} database of known multicomponent Ag and Cu oxides, without restrictions on element composition, to search for new candidate TCOs. We indexed all the compounds in this database by applying selected crystal structure descriptors as structure type, stoichiometry, and coordination environment of the Cu and Ag cations. Chemical insight points to a significant likelihood that 2- and 4-fold coordination of the noble metal cations yield band structure properties suitable for the transparency and hole conductivity needed in TCOs. We scanned the indexed database to find compounds that could match these requirements and identified a set of materials that could be interesting candidate {\em p}-type TCOs. [Preview Abstract] |
Tuesday, March 22, 2011 12:03PM - 12:15PM |
J28.00003: Ab-Initio Prediction of Phase Diagrams Using a Genetic Algorithm Will Tipton, Richard Hennig The computational design and prediction of materials' properties is a goal on which much progress has been made. However, it is generally necessary to first determine a material's crystal structure, and this remains a difficult problem. Previously, genetic algorithms have been successful in searching for stable crystal structures at particular compositions. However, when approaching a new material system, it is often unknown at which compositions stable structures might form. In order to search all of composition space simultaneously, Trimarchi and Zunger have recently suggested a modification to the traditional GA approach. In this method candidate structures are evaluated according to their formation energies with repect to structure found previously. We have implemented this technique in our genetic algorithm code and are investigating the practical details of its use. We have predicted previously-unknown phases in the Li-Be and elemental Eu systems under high pressure. [Preview Abstract] |
Tuesday, March 22, 2011 12:15PM - 12:27PM |
J28.00004: The Harvard Clean Energy Project. Large-scale computational screening and design of molecular motifs for organic photovoltaics on the World Community Grid Johannes Hachmann, Roberto Olivares-Amaya, Sule Atahan-Evrenk, Carlos Amador-Bedolla, Alan Aspuru-Guzik Organic solar cells are one of the promising approaches to ubiquitously establishing renewable energy sources; alas the necessary 10\% energy conversion efficiency remains elusive. We present the Harvard Clean Energy Project (CEP, http://cleanenergy.harvard.edu) which is concerned with the screening and design of organic photovoltaics (and organic electronics in general) by means of first-principles computational quantum chemistry. We use modern DFT to assess the quality of candidate structures and systematically improve upon these based on the gathered understanding of structure-property relations. The CEP is a high-throughput investigation which utilizes the massive computational resource of the IBM World Community Grid, which allows us to characterize millions molecules of interest in the course of the next year. We address the combinatorial generation of our molecular library, our database, workflow organization and automation, data calibration and cheminformatics analysis, and the closure of the development cycle provided by our experimental collaborators. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 1:03PM |
J28.00005: Computational design of new A2BX4 materials Invited Speaker: The A2BX4 family of ternary compounds represents an important class of materials. Members of this group, in addition to being among the earth most abundant materials, also span a significant range of physical properties including ferromagnetism, coexistence of transparency and p-type conductivity, ferroelectricity, etc. Today we know for about 800 A2BX4 compounds that have been characterized experimentally. This is only a portion of nearly 5000 A2BX4 combinations that could be constructed throughout the periodic table. In this talk I will present a systematic theoretical approach, based on ab initio calculations, for predicting new A2BX4 compounds. For a given new A2BX4 combination we find the candidate crystal structures from the classification of the existing A2BX4 in terms of the atomic orbital radii of the constituent A and B atoms (Zhang and Zunger, Adv. Funct. Mat. 20, 1944, 2010). This step is followed by the set of high-throughput ab initio calculations which are used to sort out the ground-state structure and compute the corresponding heat of formation. The stability of a given A2BX4 with respect to decomposition into competing phases is then tested against all possible combinations of known compounds involving the same elements. This is done by comparing the heat of formation of the new ternary and the heats of formation of the competing (existing) binary and ternary compounds. I will also discuss the algorithms for searching the chemical space of ternary compounds in order to find the materials with target properties. [Preview Abstract] |
Tuesday, March 22, 2011 1:03PM - 1:15PM |
J28.00006: Discovering potentially overlooked Filled Tetrahedral Structure compounds by high-throughput first-principles calculation Xiuwen Zhang, Alex Zunger Filled Tetrahedral Structures (FTS) such as LiZnP are derived from the binary zincblende family by splitting a cation such as Ga in GaP into two lower-valent cations Li+Zn, placing one on the original cation site and the other on one of the empty interstitial sites. Generalizing this process, it is possible to generate a few hundred of ABX compounds. Depending on the position of A, B, and X in the periodic table, the structure of such ABX can deviate from the parent tetrahedral framework. Using high-throughput total-energy calculation in GGA+U we have examined the stable structures and possible metastable structures of a few hundred ABX compounds, establishing the basic regularities relating structure to chemical identity. Their thermodynamical stability has been checked by taking into account the competing binary and ternary phases. We identify dozens of ABX compounds likely to have large band gaps, potentially suitable as solar absorbers and transparent conductors. [Preview Abstract] |
Tuesday, March 22, 2011 1:15PM - 1:27PM |
J28.00007: GW band gap of Filled Tetrahedral Structuctures: absorbers and topological insulators ? Julien Vidal, Xiuwen Zhang, Jun-Wei Luo, Alex Zunger Filled Tetrahedral Structures (FTS) such as LiZnP are derived from the binary zincblende material such as GaP by splitting a cation such as Ga into two lower-valent cations Li+Zn, placing one on the original cation site and the other on one of the empty interstitial sites. Generalizing this process, it is possible to generate a few hundred of ABX compounds. Their electronic structure has been previously calculated by bandgap-underestimating DFT assuming a zincblende-derived crystal structure. We use instead GW to establish (i) which ABX materials are potentially suitable as absorbers in solar cells and (ii) which of the ABX materials previously proposed as topological insulators based on DFT may not be so in a better approximation such as GW. [Preview Abstract] |
Tuesday, March 22, 2011 1:27PM - 1:39PM |
J28.00008: Quantum Monte Carlo for Materials Design Tim Mueller, Lucas Wagner, Jeffrey Grossman When designing new materials it is important to have an accurate measure of the material's formation energy to assess thermodynamic stability and chemical activity. Computational materials science holds the potential to accurately predict formation energies, but widely-used methods such as density functional theory often yield large errors when calculating energy differences between compounds with significantly different electronic structures. More accurate quantum chemical methods tend to scale poorly with system size, making it infeasible to apply them to many materials. One exception is quantum Monte Carlo (QMC), which effectively scales linearly or better with system size when calculating formation energy per atom. QMC scales perfectly with the number of processors, making it ideally positioned to take advantage of the rapidly growing core count in central and graphics processing units. It has been shown that quantum Monte Carlo can successfully predict formation energies for some solid state materials, but a broad assessment has been lacking. We have run QMC calculations on a variety of different materials for which high-quality experimental data exists. We present data on the cost and accuracy of QMC, providing insight into the role QMC will play in materials design. [Preview Abstract] |
Tuesday, March 22, 2011 1:39PM - 1:51PM |
J28.00009: Off-lattice self-learning kinetic Monte Carlo: application to 3D island decay on fcc(100) surface Giridhar Nandipati, Abdelkader Kara, Syed Islamuddin Shah, Talat S. Rahman We report the development of an off-lattice kinetic Monte Carlo (KMC) method with a new three-dimensional (3D) pattern recognition scheme to better identify the local environment and processes involving 3D motion which was not possible in the earlier approach [1]. In the present scheme, to uniquely identify the 3D neighborhood around the central atom or leading atom we split it into 3D rectangular boxes whose dimensions dictate the accuracy with which the motion of the diffusing entity to be accounted. This technique combines the idea of self-learning KMC (SLKMC) [2] method with the new pattern-recognition scheme fitted to an off-lattice model. We present application of this off-lattice SLKMC to 3D island decay on fcc (100) surface and compare the results and computational efficiency to that available in the literature. \\[4pt] [1] A. Kara et al, J. Phys.: Condens. Matter, 21 (2009)\\[0pt] [2] O. Trushin et al, Phys. Rev. B, 72, 115401 (2005) [Preview Abstract] |
Tuesday, March 22, 2011 1:51PM - 2:03PM |
J28.00010: Density-functional study of U-Mo alloys Alexander Landa, Per Soderlind, Patrice E.A. Turchi The U-Mo and U-Zr alloys proved to be very promising fuels for advanced fast nuclear reactors. According to numerous experiments, the main advantages of U-Mo fuels over U-Zr fuels lies in a much lower constituent redistribution due to the existence a single $\gamma $-U-Mo phase with body-centered cubic structure over typical fuel operation temperatures. Density-functional theory (EMTO-CPA technique) previously used to describe phase equilibria in U-Zr alloys [A. Landa, P. S\"oderlind, P. E. A. Turchi, Journal of Alloys and Compounds, 478 (2009) 103] is extended to investigate the ground-state properties of U-Mo solid solutions. Calculated heats of formation of bcc U-Zr and U-Mo alloys are compared with CALPHAD assessments. We discuss how the heat of formation in both alloys correlates with the charge transfer between the alloy components, and how the specific behavior of the density of states in the vicinity of the Fermi level promotes the stabilization of the U$_{2}$Mo compound. Our calculations prove that, due to the existence of a single $\gamma $-phase over the typical fuel operation temperatures, $\gamma $-U-Mo alloys should indeed have much lower constituent redistribution than $\gamma $-U-Zr alloys for which binodal decomposition causes a high degree of constituent redistribution. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, March 22, 2011 2:03PM - 2:15PM |
J28.00011: Inverse band design of SiGe superlattices with direct band-gaps Mayeul d'Avezac, Jun-Wei Luo, Alex Zunger, Thomas Chanier Integrating optoelectronic functionalities directly into the mature Silicon-Germanium technology base would prove invaluable for many applications. Unfortunately, both Si and Ge display indirect band-gaps unsuitable for optical applications. It was previously shown (Zachai \textit{et al.} PRL \textbf{64} (1990)) that epitaxially grown [(Si)$_n$(Ge)$_m$]$_p$ (i.~e.~ a single repeat unit) grown on Si can form direc-gap heterostructures with weak optical transitions as a result of zone folding and quantum confinement. The much richer space of \emph{multiple-period} superlattices [(Si)$_{n_1}$(Ge)$_{n_2}$(Si)$_{n_3}$(Ge)$_{n_4}$\ldots$Ge_{n_N}$]$_p$ has not been considered. If $M=\sum n_i$ is the total number of monolayers, then there are, roughly, $2^M$ different possible superlattices. To explore this large space, we combine a (i) genetic algorithm for effective configurational search with (ii) empirical pseudopotential designed to accurately reproduce the inter-valley and spin-orbit splittings, as well as hydrostatic and biaxial strains. We will present multiple-period SiGe superlattices with large electric dipole moments and direct gaps at $\Gamma$ yielded by this search. [Preview Abstract] |
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