Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session B23: Computational Materials Discovery and Design - Electronic StructureFocus
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Sponsoring Units: DMP DCOMP Chair: Sahar Sharifzadeh, Boston University Room: 322 |
Monday, March 14, 2016 11:15AM - 11:51AM |
B23.00001: Materials by design: methodological developments in the calculation of excited-state properties Invited Speaker: Marco Govoni Density functional theory (DFT) is one of the main tools used in first principle simulations of materials; however several of the current approximations of exchange and correlation functionals do not provide the level of accuracy required for predictive calculations of excited state properties. The application to heterogeneous systems of more accurate post-DFT approaches such as Many-Body Perturbation Theory (MBPT) -- for example to nanostructured, disordered, and defective materials -- has been hindered by high computational costs. In this talk recent methodological developments in MBPT calculations will be discussed, as recently implemented in the open source code WEST [1], which efficiently exploits HPC architectures. Results using a formulation that does not require the explicit calculation of virtual states, nor the storage and inversion of large dielectric matrices will be presented; these results include quasi particle energies for systems with thousands of electrons and encompass the electronic structure of aqueous solutions, spin defects in insulators, and benchmarks for molecules and solids containing heavy elements. Simplifications of MBPT calculations based on the use of static response properties, such as dielectric-dependent hybrid functionals [2], will also be discussed.\\ [4pt][1] www.west-code.org; M. Govoni, and G. Galli, J. Chem. Theory Comput. 11, 2680 (2015)\\ [0pt][2] J.H. Skone, M. Govoni, and G. Galli, Phys. Rev. B 89, 195112 (2014) [Preview Abstract] |
Monday, March 14, 2016 11:51AM - 12:03PM |
B23.00002: An Automated Ab Initio Approach for Identifying Small Band Gap Ferroelectric Tess Smidt, Sebastian Reyes-Lillo, Jeffrey Neaton Small band gap ferroelectrics are scarce and yet hold promise for optoelectronics applications. In this work, we leverage the electronic and symmetry requirements that give rise to ferroelectricity to search for new small band gap ferroelectrics using the Materials Project and Inorganic Crystal Structure Database. We create an automated workflow that combines database queries, symmetry tools and high-throughput DFT to identify candidate classes of ferroelectrics. Using density functional theory and beyond, we reveal accurate band gap trends for new and previously synthesized compounds. The effect of chemical doping on the polarization and energy barrier is discussed for select cases. [Preview Abstract] |
Monday, March 14, 2016 12:03PM - 12:15PM |
B23.00003: Ab initio parametrization of bond-polarizability model for Raman spectroscopy of complex Si materials David A. Strubbe, Jeffrey C. Grossman Classical inter-atomic potentials can be successful at predicting the vibrations of materials at system sizes intractable by quantum methods. However, to predict Raman spectra, electrons must be re-introduced, for example via a bond-polarizability model which attributes the polarizability to cylindrically symmetrical inter-atomic bonds. Parameters in assumed functional forms are fit to experimental spectra, and then a Raman intensity can be computed for each mode. In the case of amorphous silicon, the existing models do not show satisfactory agreement with experimental spectra. To generate a more accurate and transferable bond-polarizability model, we have instead begun with ab initio calculated Raman tensors for a set of a-Si:H structures [DA Strubbe et al., arXiV:1511.01139]. This atomistic data set allows us to obtain parameters and functional forms for a general model, without confounding errors from the potentials. This Raman model can be used to study large structural models with relevance for photovoltaics, such as medium- and long-range order in a-Si:H, nanocrystalline Si, amorphous/crystalline interfaces, or a-Si:H nanowires, at sizes that would be inaccessible for ab initio calculations. We analyze the applicability of this approach to other materials systems. [Preview Abstract] |
Monday, March 14, 2016 12:15PM - 12:27PM |
B23.00004: Self-consistent perturbation theory for two dimensional twisted bilayers Sharmila N. Shirodkar, Georgios A. Tritsaris, Efthimios Kaxiras Theoretical modeling and ab-initio simulations of two dimensional heterostructures with arbitrary angles of rotation between layers involve unrealistically large and expensive calculations. To overcome this shortcoming, we develop a methodology for weakly interacting heterostructures that treats the effect of one layer on the other as perturbation, and restricts the calculations to their primitive cells \footnote{Georgios A. Tritsaris {\it et. al.}, Perturbation theory for weakly coupled two-dimensional layers, \textbf{under review.}}. Thus, avoiding computationally expensive supercells. We start by approximating the interaction potential between the twisted bilayers to that of a hypothetical configuration (viz. ideally stacked untwisted layers), which produces band structures in reasonable agreement with full-scale ab-initio calculations for commensurate and twisted bilayers of graphene (Gr) and Gr/hexagonal boron nitride (h-BN) heterostructures. We then self-consistently calculate the charge density and hence, interaction potential of the heterostructures. In this work, we test our model for bilayers of various combinations of Gr, h-BN and transition metal dichalcogenides, and discuss the advantages and shortcomings of the self-consistently calculated interaction potential. [Preview Abstract] |
Monday, March 14, 2016 12:27PM - 12:39PM |
B23.00005: Simplified Quantum Transport Theory for Finite Bias and Temperature Xiaoguang Zhang, Yuning Wu, Sokrates Pantelides We reformulate the Landauer-Buttiker formula for quantum transport by explicitly accounting for the energy and bias voltage dependence of the transmission probability. Under the assumption of a constant electric field, a simple formula for the differential conductance under a finite bias and at a finite temperature is derived that does not require a nonequilibrium self-consistent calculation. Calculation for the tunneling current through Au-Benzendithiol-Au molecular junction shows excellent agreement with the nonequilibrium Green's function (NEGF) method at zero temperature. Temperature dependent I-V curves for a number of devices are demonstrated. [Preview Abstract] |
Monday, March 14, 2016 12:39PM - 12:51PM |
B23.00006: High-throughput determination of Hubbard U for cubic perovskites using the ACBN0 functional. Laalitha Liyanage, Andrew Supka, Priya Gopal, Luis Agapito, Gus Hart, Marco Fornari, Stefano Curtarolo, Marco Buongiorno Nardelli High-throughput (HT) density functional theory (DFT) computations are the method of choice for rapid screening of materials properties and materials development. However, traditional DFT is not adequate for the investigation of all systems. For materials containing transition metal elements, methods such as DFT$+$U or hybrid functionals are needed for an accurate prediction of the electronic structure. As an efficient and accurate alternative we have recently introduced the ACBN0 functional for DFT as a new pseudo-hybrid Hubbard density functional that is a parameter-free extension of traditional DFT$+$U that has been proved to correct both the band gap and the relative position of the different bands in transition metal compounds. We implemented ACBN0 in a Medium-Throughput Framework (MTFrame) designed to automate DFT calculations for systems that share a single reference crystal structure. Using the MTFrame, we have determined the effective U values for 3969 cubic perovskites (ABO3) built by permutating 63 different elements in the A and B sites. Analysis of resulting data reveals the effects of Hubbard U on the electronic properties and crystal structure. Finally, machine learning algorithms are used to find correlations in the extracted data and the U values. [Preview Abstract] |
Monday, March 14, 2016 12:51PM - 1:03PM |
B23.00007: A tool for accelerating material calculations through the generation of highly efficient $k$-point grids Tim Mueller, Pandu Wisesa The calculation of many material properties requires the evaluation of an integral over the Brillouin zone, which is commonly approximated by sampling a regular grid of points, known as $k$-points, in reciprocal space. We have developed an automated tool for generating $k$-point grids that significantly accelerates the calculation of material properties compared to commonly used methods. Our tool, which is being made freely available to the public, is capable of generating highly efficient $k$-point grids in a fraction of a second for any crystalline material. We present an overview of our method, benchmark results, and a discussion of how it can be integrated into a high-throughput computing environment. [Preview Abstract] |
Monday, March 14, 2016 1:03PM - 1:39PM |
B23.00008: Advancing Efficient All-Electron Electronic Structure Methods Based on Numeric Atom-Centered Orbitals for Energy Related Materials Invited Speaker: Volker Blum This talk describes recent advances of a general, efficient, accurate all-electron electronic theory approach based on numeric atom-centered orbitals; emphasis is placed on developments related to materials for energy conversion and their discovery. For total energies and electron band structures, we show that the overall accuracy is on par with the best benchmark quality codes for materials, but scalable to large system sizes (1,000s of atoms) and amenable to both periodic and non-periodic simulations. A recent localized resolution-of-identity approach for the Coulomb operator enables $O(N)$ hybrid functional based descriptions of the electronic structure of non-periodic and periodic systems, shown for supercell sizes up to 1,000 atoms; the same approach yields accurate results for many-body perturbation theory as well. For molecular systems, we also show how many-body perturbation theory for charged and neutral quasiparticle excitation energies can be efficiently yet accurately applied using basis sets of computationally manageable size. Finally, the talk highlights applications to the electronic structure of hybrid organic-inorganic perovskite materials, as well as to graphene-based substrates for possible future transition metal compound based electrocatalyst materials. [Preview Abstract] |
Monday, March 14, 2016 1:39PM - 1:51PM |
B23.00009: Simple Rules for Solid-state Design: From Bulk to Interface Keith Butler, Aron Walsh, Adam Jackson, Dan Davies, Fumiyasu Oba, Yu Kumagai High-throughput screening enterprises such as Materials Project and the OQMD are well suited to the application of density functional theory for assessing the merits of known bulk materials. The blind exploration of the new combinations and permutations of the periodic table is a daunting task, to paraphrase Samuel Beckett we feel \textit{lost before the confusion of innumerable prospects}. Centuries of research have provided us with myriad rules for assessing the feasibility of a given stoichiometry and the likelihood of particular crystal arrangements. We explore the ways in which chemical knowledge and state-of-the-art computational physics can be combined to accelerate materials design. We present the SMACT (Semiconducting Materials by Analogy and Chemical Theory) package, which combines these rules with searching of chemical space to predict plausible and heretofore unknown compounds. I will then provide some illustrative examples of materials' design focusing on several important issues: (i) designing new photovoltaic materials [1], (ii) the role of surfaces and polymorphism in controlling electronic properties [2,3], and (iii) the design of porous materials [4]. [1] K. T. Butler et al., \textit{Energy Environ. Sci.}, \textbf{2015}, 8, 838 [2] K T. Butler et al., \textit{Phys. Rev. B}, \textbf{2014}, 89, 115320 [3] J. Buckeridge, et al., \textit{Chem. Mater.}, \textbf{2015}, 27, 3844 [4] K. T. Butler, et al., \textit{J. Am. Chem. Soc.},\textbf{ 2014}, 136, 2703 [Preview Abstract] |
Monday, March 14, 2016 1:51PM - 2:03PM |
B23.00010: ACBN0-tool for accelerated materials discovery. Priya Gopal, Laalitha Liyanage, Luis Agapito, Seunghun Lee, Ichiro Takeuchi, Gus Hart, Stefano Curtarolo, Marco Fornari, Marco Buongiorno Nardelli High-Throughput QM computation of material properties by abinitio methods has become the foundation of an effective approach to materials design. One of the major challenges in mapping the materials genome is in developing efficient computational tools that are cost-effective and accurate at the same time. In this talk, we discuss the newly developed ACBN0 pseudo-hybrid Hubbard density functional where the Hubbard energy within the DFT $+$ U formulation is calculated self consistently. The U depends on the electron density and depends both on the geometry and chemical environment of the system. We show that ACBN0 improves the description of both the structural and electronic properties in a range of complex materials from Zn/Cd based chalcogenides to the TMOs. The magnetic properties are better described compared to the LDA/GGA functionals. We will also discuss the application of the ACBN0 approach to surfaces, doped and multi-valent systems where it is possible to evaluate U for different sites and chemical bonding. For all the complex materials studied here, we find that the electronic properties are significantly improved over the DFT values and the accuracy is at par with the HSE values at a fraction of the computational cost. [Preview Abstract] |
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