Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V12: Computational Materials Design - Prediction of Novel Phases |
Hide Abstracts |
Sponsoring Units: DMP DCOMP Room: LACC 303B |
Thursday, March 8, 2018 2:30PM - 2:42PM |
V12.00001: Prediction of a new phosphorus allotrope with tunable direct band gap and high mobility Woo Hyun Han, Sunghyun Kim, In-Ho Lee, Kee Joo Chang Black phosphorus can be exfoliated to a few layers, belonging to the class of 2D materials. Thin black phosphorus has received much attention because of it high carrier mobility and moderate band gap which are promising for applications to nanoelectronic and nanophotonic devices. Besides black phosphorus, phosphorus can exist in many different forms in nature. Recently, blue phosphorus has been theoretically predicted and subsequently synthesized on gold substrate by experiments. The existence of a variety of phosphorus allotropes motivates our work to search for a new allotrope that provides more interesting characteristics than black phosphorus. Here, we report the prediction of a new P allotrope, called green phosphorus, using an evolutionary crystal structure search method. Green phosphorus has a layered structure with the interlayer interaction comparable to that of black phosphorus. Thus, it should be exfoliated to a few layers. As the film thickness decreases to a monolayer, green phosphorus exhibits strong anisotropy in the optical and transport properties. Due to the tunable direct band gap, green phosphorus is suitable for nanodevice applications. We discuss the effects of temperature and substrate on the possible synthesis of green phosphorus. |
Thursday, March 8, 2018 2:42PM - 2:54PM |
V12.00002: An accurate predictive framework for the experimental realizability of metastable polymorphs Eric Jones, Vladan Stevanovic Exploring structural degrees of freedom at fixed chemical composition appears to be a promising avenue forward in the search for new functional materials. However, not every low-energy polymorph discovered on a computer stands an equal chance at being synthesized in the laboratory. We propose a statistical mean field model of polymorph formation wherein the probability that a polymorph will be experimentally realized under near-equilibrium conditions is shown mathematically to depend upon both the hypervolume of that structure's potential energy basin of attraction and a Boltzmann factor weight containing the polymorph's potential enthalpy per particle. We apply our model principally to elemental silicon, where dozens of theoretical metastable structures have been proposed but only a few have been realized. Our model, along with estimates of enthalpies and basin hypervolumes obtained from density functional theory relaxations of random structures, accounts for the metastable polymorphism displayed by silicon to the exclusion of a very large number of other theoretical low-energy structures. The model thus constitutes a screening procedure to drastically reduce the number of polymorphs, which need to be considered for kinetics analysis and experimental synthesis. |
Thursday, March 8, 2018 2:54PM - 3:06PM |
V12.00003: Phase Stability of High-Pressure Materials Maximilian Amsler, Vinay Hegde, Christopher Wolverton Recent advances in high-pressure techniques have led to the discovery of numerous new materials with exciting properties, ranging from unexpected stoichiometries in simple systems to reports of record breaking superconductivity in hydride materials. Since the in situ characterization of materials at extreme pressures is challenging, computational tools have become increasingly valuable to guide experiments. Crystal structure prediction (CSP) methods in conjunction with ab initio calculations are commonly used to assess the composition, structure, and properties of high-pressure compounds. However, such calculations are computationally very demanding, often limiting the discovery efforts to small systems with moderate chemical complexity. Here, we present a novel method to search for high-pressure materials on a large scale by combining a data-driven screening approach with a CSP algorithm. Based on available materials data in the Open Quantum Materials Database, we successfully predict many new high-pressure compounds, and demonstrate that our model can explain the occurrence of phases in nature that are not ground states at ambient conditions. |
Thursday, March 8, 2018 3:06PM - 3:18PM |
V12.00004: A Generalized Convex Hull Construction for Computational Materials Discovery Edgar Engel, Andrea Anelli, Michele Ceriotti Structure searches typically generate intractably large databases of locally-stable structures. Before determining accurate structural properties and synthesis pathways one must first identify those that can be synthesized (and are of practical interest). |
Thursday, March 8, 2018 3:18PM - 3:30PM |
V12.00005: Dynamic polymorphism in solids with multiple local minima on the atomic potential energy surface Nikolai Zarkevich, Duane Johnson, Vitalij Pecharsky Polymorphic solids of the same chemical composition can have different atomic structures. If transformations to other structures have sufficiently high enthalpy barriers, then each structure is either stable or metastable: it is stationary and does not spontaneously change with time. But what happens, if those barriers are low? As examples, we consider NiTi and FeRh alloys exhibiting large elasto-caloric and magneto-caloric effects. We suggest a model for dynamically polymorphic solids, consider an atomic structure stabilized by entropy, and compare theoretical predictions to experimental observations. |
Thursday, March 8, 2018 3:30PM - 3:42PM |
V12.00006: Towards controlled morphology of bimetallic nanoparticles: Concentration and size effects Javier Rojas, Eduardo Bringa, Rafael Gonzalez, Sebastian Allende, Samuel Baltazar Bimetallic nanoparticles can be tailored by varying the concentration of their constituent elements, resulting in novel structures and/or configurations, leading to interesting electronic, mechanical and chemical properties. A theoretical method, is implemented to find optimized morphology of nanoparticles in bimetallic particles such as FeCu, FeCo, CuNi systems. These searching routines were applied to different materials and initial configurations at different size and concentrations. Additionally, a continuous model is proposed to calculate the energies of the energetically stable structures, and determine the morphology transition between Core-Shell and Janus-like nanoparticles, a result in agreement with experimental evidence. These approaches can help to the design of novel materials with specific properties for technological applications. |
Thursday, March 8, 2018 3:42PM - 3:54PM |
V12.00007: Simulation of Grain Boundary Kinetics in HCP Nanocrystals Using the Structural Phase-field Crystal (XPFC) model Jason Luce, Katsuyo Thornton The phase-field crystal (PFC) model can be applied to study material phenomena at atomic length-scales and diffusive time-scales, bridging the gap between atomistic and mesoscale models. In a previous study, the PFC model has been used to investigate grain boundary motion and grain rotation in BCC crystals [1]. In this study, the structural phase-field crystal (XPFC) model is used to simulate grain boundary dynamics of hexagonal close-packed (HCP) nanocrystals, which is of great interest in the field of lightweight materials design. HCP grain boundaries structures are generated using the XPFC model, where the free energy of the model has been parameterized so that simulated grain boundary energies (GBEs) show agreement with molecular dynamics simulations of symmetric tilt grain boundaries in Mg [2]. This parameterized XPFC model is used to predict nanoscale grain boundary kinetic phenomena (e.g., grain boundary motion and grain rotation) associated with HCP grain boundaries. |
Thursday, March 8, 2018 3:54PM - 4:06PM |
V12.00008: Grain Growth Prediction Based on Data Assimilation by Implementing 4DVar on Phase-Field Models Shin-ichi Ito, Hiromichi Nagao, Tadashi Kasuya, Junya Inoue We propose a method to predict grain growth based on data assimilation by using a four-dimensional variational method (4DVar). The method utilizing a second-order adjoint method, compared with conventional data assimilation methods, can drastically save the computational cost needed to obtain the estimates and uncertainties of parameters involved in phase-field models. When implemented on a multi-phase-field model, the proposed method allows us to calculate the predicted grain structures and uncertainties in them that depend on the quality and quantity of the observational data. We confirm through numerical tests involving synthetic data that the proposed method correctly reproduces the true phase-field assumed in advance. Furthermore, it successfully quantifies uncertainties in the predicted grain structures, where such uncertainty quantifications provide valuable information to optimize the experimental design. |
Thursday, March 8, 2018 4:06PM - 4:18PM |
V12.00009: Mesoscale modeling of mixed-type dislocations in face-centered cubic metals Shuozhi Xu, Jaber Mianroodi, Yuanqi Guo, Ruifeng Zhang, Abigail Hunter, Irene Beyerlein, Bob Svendsen Mixed-type dislocations are prevalent in face-centered cubic metals and play an important role in plastic deformation. Their key characteristics, such as the core structure and core energy, cannot simply be extrapolated from those of dislocations with 0^{o} and 90^{o} (screw/edge) character angles. Most studies, however, have been devoted to those of pure edge/screw type. In this work, we explore the core structure/energy/stress of mixed-type dislocations in Al using a variety of meso-scale dislocation models, i.e., phase-field dislocation dynamics, atomistic phase-field microelasticity, and concurrent atomistic-continuum modeling. The generalized stacking fault energy surface for Al is calculated using density functional theory and employed in the phase field modeling. Two atomic-level stress formulations are employed and compared. The issues of core energy double counting in phase field methods and grid/mesh sensitivity are explored. We then benchmark results against molecular statics and discuss possible sources of errors in these continuum calculations. A dislocation loop is then modelled using these approaches to shed light on their abilities to describe more realistic mixed-type configurations, potentially assisting in designing stronger metallic materials. |
Thursday, March 8, 2018 4:18PM - 4:30PM |
V12.00010: Lateral and Vertical Heterostructures of h-GaN/h-AlN: Electron Confinement, Band Lineup and Quantum Structures Engin Durgun, Abdullatif Onen, Deniz Kecik, Salim Ciraci Lateral and vertical heterostructures constructed of 2D h-GaN and h-AlN display novel electronic and optical properties and diverse quantum structures to be utilized in 2D device applications. Lateral heterostructures formed by periodically repeating narrow h-GaN and h-AlN stripes and direct-indirect characters of the band gaps and their values vary with the widths of these stripes. However, for wider sizes, 1D multiple quantum well structures can be generated with confinement of electrons and holes. Vertical heterostructures formed by thin stacks of h-GaN and h-AlN are composite semiconductors with tunable band gap. However, depending on the stacking and number of layers, the vertical heterostructure can transform into a junction, which displays staggered band alignment. Despite the complexities due to confinement effects and charge transfer across the interface, the band diagrams of the heterostructures are conveniently revealed from the electronic structure projected to the atoms or layers. It is also shown that the optical properties attained in lateral and vertical heterostructures are rather different from their single-layer parent constituents. |
Thursday, March 8, 2018 4:30PM - 4:42PM |
V12.00011: Composition-Dependent Phase Stability in Yttria Stabilized Zirconia: Clues from Lattice Dynamics Calculation Jongmin Yun, Ji-Hwan Lee, Emin Kilic, Aloysius Soon Yttria-stabilized zirconia (YSZ) is one of the widely-used thermal barrier coating (TBC) materials in gas-turbine engine applications at high operating temperatures. It is well reported that the thermal cycle life of these oxide coatings is highly sensitive to the concentration of yttria introduced in YSZ. In particular, at approximately 3 to 4 mol% of yttria in YSZ, it was proposed that this concentration of yttria yields the longest thermal cycle life and may have strong correlations to its preferred crystal phase (cubic (c) or tetragonal (t)) and mechanical strength. However, a careful and systematic study of the spectroscopic fingerprints of low-yttria YSZ is still lacking, and knowledge gained here will be very useful for the future design of more durable YSZ-based TBCs. Using first-principles density-functional theory calculations, we examine the lattice dynamics of c-YSZ and t-YSZ for low Y_{2}O_{3} mol%, supplementing our structural analysis information with simulated X-ray diffraction and pair distribution function results to explain new inelastic neutron scattering experiments. |
Thursday, March 8, 2018 4:42PM - 4:54PM |
V12.00012: First-Principles Exploration of Thermodynamically Stable Cs-O Compounds Jinseon Park, Lizhi Zhang, Mina Yoon Cesium oxides, well-established low work function materials, have been used as surface coating and interfacial layer substances to improve the performance of photocathodes, thermionic energy converters, light-emitting devices, and solar cells. Cesium oxide compounds (Cs_{x}O_{y}) exist in many different stoichiometries with high air sensitivity, thus it remains a challenge to understand from experimental data their structural properties and resultant electronic properties. We performed global structure searches of Cs–O compounds with different stoichiometries (CsO, Cs_{2}O, CsO_{2}, and Cs_{3}O) by using a particle swarm optimization algorithm coupled with first-principles total energies. For each composition, stable structures of 5 ~ 8 different space groups were identified in the energy range about 10 meV/atom from the lowest energy configurations, which reflects the complicated phases of Cs–O beyond those in the literature. Our first-principles calculations unravel the correlation between the structures’ stoichiometries and symmetries and the resulting electronic structures, such as band gaps and work functions. Our results are expected to provide a route to improving the functional properties of cesium oxides for various device applications. |
Thursday, March 8, 2018 4:54PM - 5:06PM |
V12.00013: Comparing the performance of Monkhorst-Pack and Chadi-Cohen k-point grids Pandu Wisesa, Tim Mueller The calculation of material properties often utilizes a grid of points, known as k-points, to approximate an integral in reciprocal space. The choice of grids can greatly influence the accuracy of the calculation and its computational cost. Monkhorst-Pack grids with the shift vector of (1/2, 1/2, 1/2) are widely used due to their efficiency. However, this shift vector can break symmetry when applied to structures with trigonal or hexagonal crystal systems, which can be resolved by using a shift vector of (0, 0, 1/2). An alternative is to use Chadi-Cohen type hexagonal grids. We present a quantitative comparison of these two types of grids, looking at their performance for materials with trigonal or hexagonal symmetry. We also discuss updates to the k-point grid server such as new features and additional software package support. |
Thursday, March 8, 2018 5:06PM - 5:18PM |
V12.00014: Effect of vacancy ordering in metastable Ge-Sb-Te phase-change materials Young-Sun Song, Youngjae Choi, Sang-Hoon Lee, Seung-Hoon Jhi Chalcogenide ternary compounds Ge_{2}Sb_{2}Te_{5} (GST) are well-known phase-change materials that exhibit fast structural transition between amorphous and crystalline phases. Metastable (m-)GST, its crystalline phase, is a distorted NaCl structure with 4(b) sites occupied by 40% Ge, 40% Sb, and 20% vacancies. Atomic configuration of 4(b) sites, especially the distribution of vacancy, is known to be crucial not only for phase-change process but also to the electrical transition such as Anderson localization. Despite its significance, consensus on the 4(b)-site configuration is yet to be established. In this talk, we present the effect of vacancy ordering in m-GST on material properties. We calculated energetics of m-GST for various vacancy configurations using first-principles calculations and tight-binding method. For quantitative analysis of the relationship between vacancy distribution and energetic stability, we established a set of parameters that quantify the degree of vacancy disorder in m-GST to identify key structural features that govern the system’s energy and electrical conductivity. Correlation between annealing temperature and vacancy ordering of m-GST was also investigated using molecular dynamics simulations. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2019 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700