Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session K23: Focus Topic: Computational Materials Discovery and Design  Structure Prediction and Phase DiagramsFocus

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Sponsoring Units: DMP DCOMP Chair: Stephan Lany, National Renewable Energy Laboratory Room: 322 
Wednesday, March 16, 2016 8:00AM  8:36AM 
K23.00001: Entropy descriptors and Entropy Stabilized Oxides Invited Speaker: Stefano Curtarolo In this presentation we will discuss the development of entropy descriptors for the AFLOWLIB.org abinitio repository and the path leading to the synthesis of the novel entropy stabilized oxides. [Nat. Comm. 6:8485 (2015)]. Research sponsored by DODONR N000141310635 and N000141512863. [Preview Abstract] 
Wednesday, March 16, 2016 8:36AM  8:48AM 
K23.00002: Computational Discovery of New Heusler Compounds: Structures, Stabilities, and Applications Jiangang He, Vinay Hegde, Chris Wolverton Since their discovery by Fritz Heusler in 1903, Heusler compounds, X$_2$YZ, have been attracting a lot of research attention and have been intensely studied for their potential usage in spintronics, shapememory devices, superconductors, thermoelectrics, topological insulators, and other applications. However, although more than 1000 Heusler compounds have been reported experimentally or computationally, a lot of potential Heusler compounds have not been explored yet due to complexities involved in dealing with such a huge phase space. As searching for new compounds experimentally is an expensive and a lengthy process, in this talk, we will demonstrate how to use a multistep highthroughput computational screening method to predict several hundreds new stable and metastable Heusler compounds from 186588 compositions. As an example application, we will illustrate how to find age hardening precipitates using our screening strategy [Preview Abstract] 
Wednesday, March 16, 2016 8:48AM  9:00AM 
K23.00003: Discovering complete pressuretemperature phase diagrams with Hamiltonian Monte Carlo nested sampling Robert Baldock, Noam Bernstein, Livia Bart\'okPart\'ay, G\'abor Cs\'anyi Nested sampling is a Monte Carlo algorithm that can be used to efficiently calculate the complete configurational density of states in a material that undergoes multiple firstorder phase transitions. From the density of states one can calculate the partition function as an explicit function of temperature and perform statistical mechanics from first principles. Indeed, we have shown how nested sampling can be used to automatically discover complete pressuretemperature phase diagrams with no prior knowledge of the locations of phase transitions or the structures of phases. In this talk I will present a new version of the nested sampling algorithm, based on a modified Hamiltonian (``Hybrid'') Monte Carlo scheme. This new scheme reduces the scaling of a general nested sampling calculation. In particular the new algorithm expedites the sampling of atomic configuration spaces in condensed phases, and permits one to perform nested sampling calculations at a fraction of the cost required by ordinary nested sampling with standard Monte Carlo. [Preview Abstract] 
Wednesday, March 16, 2016 9:00AM  9:12AM 
K23.00004: Equilibrium phase diagrams of alloys using nested sampling Noam Bernstein, Robert J N Baldock, Livia Bart\'okPart\'ay, G\'abor Cs\'anyi Temperaturepressurecomposition phase diagrams describe the structures of materials in thermal equilibrium, and are an essential tool in understanding material properties. Predicting phase diagrams is challenging, even given a description of the interatomic interactions, because of the need to sample a very large configuration space. Nested sampling (NS) has been shown to be an efficient tool for calculating the partition function, and therefore all thermodynamic properties and ensemble averages, by systematically sampling the configuration space of isolated and periodic systems. Its effectiveness comes from sampling starting from high energy, where barriers are relatively low and equilibration is relatively fast, and iteratively eliminating a fixed {\em fraction} of the remaining configuration space. We present an application of NS at constant pressure to the phase diagram of a model binary alloy, CuAu, using an embedded atom method potential. We identify phase transitions indicated by peaks in the calculated specific heat, and the dominant phase at each temperature from ensembleaveraged structural ordering, as represented by quantities such as the radial distribution function. These results demonstrate the power of NS as a method for calculating complete phase diagrams. [Preview Abstract] 
Wednesday, March 16, 2016 9:12AM  9:48AM 
K23.00005: Taking Materials Design Into The Space Of Polymorphs: Structure Predictions And Realizability Invited Speaker: Vladan Stevanovic The phenomenon of polymorphism exemplifies the significance of structural degrees of freedom in determining physical properties of solids. Classic case is elemental carbon with markedly different mechanical, optical and electronic properties between its graphite and diamond forms. To harness the richness of this phenomenon and extend rational materials design into the space of polymorphs, there is a need for developing approaches that are capable of exploring systematically and efficiently the potential energy surface, and (desirably) assist in experimental realization of different structures. While the former presents a common place in the field of structure predictions, less attention is given to the latter. Namely, available experimental data indicate that the energy above the ground state alone is insufficient to quantify the realizability of different structures. For example, MgO crystallizes exclusively as the rocksalt despite the predicted existence of a number of lowenergy structures. Similarly, ZnO is realized in the wurtzite, zincblende and a relatively highenergy rocksalt structure, again, apparently disregarding a number of theoretically predicted lowenergy structures. In this talk I will present recent attempts to tackle these issues focused on partially ionic systems. The structure prediction part is carried out by performing local DFT relaxations on a large set of random supperlattices (RSLs) with atoms distributed randomly over different planes in a way that favors cationanion coordination. Second, application of the RSL sampling to a range of binary ionic systems such as MgO, ZnO, SnO2 and other, reveals that the frequency of occurrence of a given structure offers an estimate of the volume of configuration space occupied by the corresponding local minimum, which is shown to be connected to the realizability of different structures. [Preview Abstract] 
Wednesday, March 16, 2016 9:48AM  10:00AM 
K23.00006: Prediction of boron carbon nitrogen phase diagram Sanxi Yao, Hantao Zhang, Michael Widom We studied the phase diagram of boron, carbon and nitrogen, including the boroncarbon and boronnitrogen binaries and the boroncarbonnitrogen ternary. Based on the idea of electron counting and using a technique of mixing similar primitive cells, we constructed many "electron precise" structures. First principles calculation is performed on these structures, with either zero or high pressures. For the BN binary, our calculation confirms that a rhmobohedral phase can be stablized at high pressure, consistent with some experimental results. For the BCN ternary, a new ground state structure is discovered and an Isinglike phase transition is suggested. Moreover, we modeled BCN ternary phase diagram and show continuous solubility from boron carbide to the boron subnitride phase. [Preview Abstract] 
Wednesday, March 16, 2016 10:00AM  10:12AM 
K23.00007: Design and discovery of heterostructural alloys Aaron Holder, Sebastian Siol, Paul Ndione, Haowei Peng, Andriy Zakutayev, Stephan Lany, Bethany Matthews, Janet Tate, Brian Gorman, Roy Gordon, Laura Schelhas, Mike Toney The tailoring of materials properties by alloying is routinely utilized to design materials for targeted technological applications. Despite the great successes of alloying in isostructural systems, heterostructural alloying remains a fundamentally unexplored area. In heterostructural alloys, the crossover between different crystal structures enables a new parameter for control over structure and properties by variation of the composition. Here, we present a complementary theoretical and experimental investigation of novel semiconducting metal chalcogenide alloys to develop design principles and approaches for utilizing heterostructural alloying as a materials design strategy. We use \textit{ab initio} methods to predict the structural and electronic properties of novel alloys with commensurate and incommensurate lattice symmetries. Nonequilibrium deposition methods are employed to overcome thermodynamic solubility limits and produce metastable thinfilm samples across the entire alloy composition range. The prediction, theoryguided combinatorial synthesis, and characterization of heterostructural alloys demonstrate the design and discovery of functional metastable materials. Our approach establishes a new route for the control of structureproperty and compositionstructure relationships by accessing nonequilibrium phase space to develop new materials with uniquely tailored properties. [Preview Abstract] 
Wednesday, March 16, 2016 10:12AM  10:24AM 
K23.00008: Informaticsaided computational design of functional layered oxides Prasanna V Balachandran, Joshua Young, Turab Lookman, James Rondinelli We discuss a datadriven \emph{ab initio} protocol with predictive capability to design and accelerate the discovery of noncentrosymmetric (NCS) inorganic oxides. Our approach synergistically integrates applied group theory, materials informatics and density functional theory (DFT) to uncover geometrychemistrysymmetry guidelines for computational design of new NCS materials, specifically oxygen octahedra containing basic building units. Using this approach, we identify new and previously unknown compositions with potential for realizing NCS structures in the bulk $n$=1 RuddlesdenPopper (RP) oxides. We then validate our predictions using DFT calculations. Our approach enables rational design and engineering of both crystal structures and functionalities. [Preview Abstract] 
Wednesday, March 16, 2016 10:24AM  10:36AM 
K23.00009: Computational Discovery of Materials Using the Firefly Algorithm Guillermo AvendañoFranco, Aldo Romero Our current ability to model physical phenomena accurately, the increase computational power and better algorithms are the driving forces behind the computational discovery and design of novel materials, allowing for virtual characterization before their realization in the laboratory. We present the implementation of a novel firefly algorithm, a populationbased algorithm for global optimization for searching the structure/composition space. This novel computationintensive approach naturally take advantage of concurrency, targeted exploration and still keeping enough diversity. We apply the new method in both periodic and nonperiodic structures and we present the implementation challenges and solutions to improve efficiency. The implementation makes use of computational materials databases and network analysis to optimize the search and get insights about the geometric structure of local minima on the energy landscape. The method has been implemented in our software PyChemia, an opensource package for materials discovery. [Preview Abstract] 
Wednesday, March 16, 2016 10:36AM  10:48AM 
K23.00010: Superconductivity in metastable phases of phosphorushydride compounds under high pressure Jose Flores Livas, Maximilian Amsler, Antonio Sanna, Christoph Heil, Lilia Boeri, Gianni Profeta, Crhis Wolverton, Stefan Goedecker, E. K. U. Gross Recently, compressed phosphine was reported to metallize at pressures above 45\,GPa, reaching a superconducting transition temperature (T$_{c}$) of 100\,K at 200\,GPa. However, neither the exact composition nor the crystal structure of the superconducting phase have been conclusively determined. In this work the phase diagram of PH$_n$ ($n=1,2,3,4,5,6$) was extensively explored by means of {\it ab initio} crystal structure prediction methods. The results do not support the existence of thermodynamically stable PH$_n$ compounds, which exhibit a tendency for elemental decomposition at high pressure even when vibrational contributions to the free energies are taken into account. Although the lowest energy phases of PH$_{1,2,3}$ display T$_{c}$'s comparable to experiments, it remains questionable if the measured values of T$_{c}$ can be fully attributed to a phasepure compound of PH$_n$. [Preview Abstract] 
Wednesday, March 16, 2016 10:48AM  11:00AM 
K23.00011: Hybrid MC/MD Method For High Entropy Alloy Bojun Feng, Michael Widom High entropy alloys (HEA) are materials that contain multiple components of elements consisting of a single solid solution phase which could make the entropy of mixing very high. From recent investigations, HEA’s possess promising properties such as strength at high temperature, tensile strength, thermal stability and corrosion resistance. In this talk, a hybrid Molecular Dynamics (MD)/Monte Carlo (MC) simulation method is introduced to the computational analysis of HEA, treating atomic displacement by MD as well as swapping atomic species by MC. This method efficiently models the phase separation and short range order by swapping between different types of atoms, while structural deviation from the perfect lattice sites of atoms is equilibrated quickly by MD. We apply this method to HfNbTaZr HEA modeled using an embeddedatom potential. The result gives a strong phase separation of HfZr and NbTa pairs shown by the pair correlation function. Diffuse scattering patterns are predicted and compared to experiments. [Preview Abstract] 
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