Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V18: Electronic Structure Methods II 
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Sponsoring Units: DCOMP Chair: Yoh Yamamoto, University of Texas, El Paso Room: BCEC 156B 
Thursday, March 7, 2019 2:30PM  2:42PM 
V18.00001: Bringing Electronic Structure Codes into the Modern Software Ecosystem Ran Adler, Andrey Kutepov, Gabriel Kotliar We propose a novel framework (“Portobello”) for assimilating Electronic Structure codes into the modern software ecosystem and facilitating an efficient software development process. First we discuss some of the pitfalls of Fortran / Python  centric paradigms, which often lead to flawed design and unwieldy code. We identify a culprit to be the lack of highlevel abstraction, which prevents reuse of components, obscures developers' intent, and hinders collaboration. Our new objectoriented framework facilitates all steps of the software developments lifecycle, and is applicable to Fortranbased systems, as well as ones written in C/C++. 
Thursday, March 7, 2019 2:42PM  2:54PM 
V18.00002: ComDMFT: a Massively Parallel Computer Package for the Electronic Structure of CorrelatedElectron Systems Sangkook Choi, Patrick Semon, Byungkyun Kang, Andrey Kutepov, Gabriel Kotliar ComDMFT is a massively parallel computational package to study the electronic structure of correlatedelectron systems (CES). Our approach is a parameterfree method based on ab initio linearized quasiparticle selfconsistent GW (LQSGW) and dynamical mean field theory (DMFT). The nonlocal part of the electronic selfenergy is treated within ab initio LQSGW and the local strong correlation is treated within DMFT. In addition to ab initio LQSGW+DMFT, charge selfconsistent LDA+DMFT methodology is also implemented, enabling multiple methods in one opensource platform for the electronic structure of CES. This package can be extended for future developments to implement other methodologies to treat CES 
Thursday, March 7, 2019 2:54PM  3:06PM 
V18.00003: Hubbard interactions from densityfunctional perturbation theory Iurii Timrov, Matteo Cococcioni, Nicola Marzari DFT+U+V is a novel and powerful tool to model systems containing partiallyfilled manifolds of localized states. However, there is a history of treating Hubbard parameters semiempirically, which is unsatisfactory. Conceptual methods to determine e.g. Hubbard U from first principles have nevertheless been introduced long ago, based either on the constrained randomphase approximation or on linear response theory. Still, these approaches are often overlooked due to their cost or complexity. Here, we introduce a computationally inexpensive and straightforward approach [1] to determine onsite U and intersite V Hubbard parameters, bypassing the need to use supercells. By recasting linearresponse susceptibilities in the language of densityfunctional perturbation theory we substitute monochromatic pertubations to supercells, and allow for a fully automated determination of Hubbard parameters in primitive cell calculations. Such developments provide the community with a robust and reliable tool to calculate consistent values of U and V for any system at hand, while opening the way for deployment in highthroughput studies. The approach is showcased with applications to the vibrational spectra of selected transitionmetal compounds. 
Thursday, March 7, 2019 3:06PM  3:18PM 
V18.00004: RESPACK software to derive ab initio effective lowenergy Hamiltonians and its extension to treat materials with strong spinorbit interaction. Maxime Charlebois, Yusuke Nomura, Yoshihide Yoshimoto, Terumasa Tadano, Masatoshi Imada, Kazuma Nakamura RESPACK [1] is an open source library that allows to calculate electron correlation effects and to derive effective lowenergy Hamiltonians starting from the density functional theory (DFT). The downfolding to lowenergy Hamiltonians is achieved by combining maximally localized Wannier functions [2] and full (or constrained) random phase approximation. It can be interfaced with both Quantum ESPRESSO [3] and xTAPP [4]. Here, we present an extension of RESPACK to treat materials with strong spin orbit effects and application to various test materials. 
Thursday, March 7, 2019 3:18PM  3:30PM 
V18.00005: Fullpotential relativistic fourcomponent Dirac–Kohn–Sham method for periodic systems using Gaussiantype functions Marius Kadek, Michal Repisky, Kenneth Ruud I will present a new fullpotential allelectron Kohn–Sham theory for obtaining fullyrelativistic band structures of spin–orbitcoupled solids. Our method is based on the fourcomponent Dirac–Coulomb Hamiltonian, and all operators are represented compactly in real space using Gaussiantype orbitals (GTOs). The local nature of GTOs allows for explicit handling of one, two, and threedimensional periodic systems avoiding the need to introduce vacuum layers. In combination with a variational treatment of spin–orbit coupling, this makes the method suitable for studying two and threedimensional topological insulators as well as spin–orbitinduced splittings of bands. The GTObased methodology makes no assumptions about the electronic density in the vicinity of nuclei, and can be used to calculate corerelated properties, such as nuclear magnetic resonance parameters. Largescale relativistic calculations of solids containing thousands of heavy atoms in the simulation supercell are possible due to the use of quaternion algebra for the timereversaladapted basis and employment of fastmultipole methods.[1] 
Thursday, March 7, 2019 3:30PM  3:42PM 
V18.00006: Densityfunctional theory for noncollinear magnetism: exact and approximate results on small Hubbard chains Edward Pluhar, Carsten Ullrich We apply a class of orbitaldependent exchangecorrelation functionals (exact exchange and SingwiTosiLandSjolander exchangecorrelation) to twoelectron systems on small Hubbard chains in the presence of noncollinear magnetic fields. We compare these approximations with benchmark results obtained from exact diagonalization and inversion of the KohnSham equation via a conjugategradient optimization. In general, good agreement is found for total energies, densities and magnetizations over a range of interaction strengths. Exchangecorrelation torques, on the other hand, are more subtle and can be difficult to approximate, especially for strong correlations. 
Thursday, March 7, 2019 3:42PM  3:54PM 
V18.00007: Metals: Automatic kpoint generation for a 60% speedup of total energy calculations Gus Hart, Wiley S Morgan, Jeremy Jorgensen, Rodney W. Forcade A generalized regular kpoint grid generation method (more general than the traditional MonkhorstPack method) leads to a 60% speedup for total energy calculations of metallic systems. Generalized regular grids can be generated using the JHU kpoint server: http://muellergroup.jhu.edu/KPoints.html. We have developed a new algorithm that can generate these same grids on the fly so that a web request is not necessary. The algorithm relies on group theoretical ideas that connect the concepts of lattices and integer matrices to yield extremely fast grid generation, enabling scans over thousands of candidate grids and select one with the highest efficiency (best kpoint symmetry reduction). 
Thursday, March 7, 2019 3:54PM  4:06PM 
V18.00008: Get 10 materials for the price of 1: computationally efficient DFT Jeremy Jorgensen, Thomas W. Sederberg, Gus Hart We have developed a numerical algorithm that will allow us to run density functional theory (DFT) computations ten times faster. Our improvements in efficiency result from accelerating the convergence rate of the band energy calculation by employing local polynomial interpolation and adaptive mesh refinement. Tests of the algorithm on 2D toy pseudopotentials show an order of magnitude improvement over the rectangular method, the method currently implemented in DFT programs. Our tests demonstrate two counterintuitive results: 1) accurately approximating the Fermi surface is critical to accurately calculate the band energy, and 2) band crossings are inconsequential. Implementing our algorithm in DFT programs will accelerate both the growth of theoretical materials databases and the discovery of materials. 
Thursday, March 7, 2019 4:06PM  4:18PM 
V18.00009: Band Unfolding Made Simple Sara García Mayo, Jose M. Soler We present a simple point of view on band unfolding of the energy bands obtained from supercell calculations that relies on the relationship existing between the local density of states in reciprocal space (qLDOS) and the fully unfolded band structure of a system. This new concept provides an intuitive and valid approach not only for periodic, but also for nontranslationally symmetric systems, as well as a way to recover the conventional band structure by doing a refolding back into the primitive Brillouin zone of the pristine crystal. We implemented this algorithm in the Siesta package and tested some of its potential applications on siliconbased systems, such as defective crystals, surfaces and amorphous structures. 
Thursday, March 7, 2019 4:18PM  4:30PM 
V18.00010: Implementation of Distortion Symmetry for the Nudged Elastic Band Method Jason Munro, Vincent Liu, Venkatraman Gopalan, Ismaila Dabo The nudged elastic band (NEB) method is an effective approach for calculating minimum energy pathways of kinetic processes. However, the final paths obtained by the algorithm rely heavily on the initially chosen path. This often necessitates running multiple calculations with different initial conditions in order to obtain reliable results. Recently, this problem has been reformulated using the language of distortion symmetry, which consists of combining static spatial symmetries with a new operation called distortion reversal, and has the property of only being conserved or raised by the NEB optimization [1]. Using this knowledge, symmetryadapted perturbations to an initial path can be generated and used to systematically lower its symmetry. By doing so, the exploration of other lowenergy pathways that may exist is enabled. The group and representation theory details behind this new approach are presented and implemented in standalone software (DiSPy). The algorithm is then demonstrated by applying it to the calculation of ferroelectric switching pathways in LiNbO_{3}. Previously reported pathways are recovered, with new paths that involve a higher degree of atomic coordination also being discovered. 
Thursday, March 7, 2019 4:30PM  4:42PM 
V18.00011: Evaluation of selfenergy matrix for electrode based on realspace pseudopotential method Shigeru Iwase, Tomoya Ono Evaluation of selfenergy matrix for electrode is one of the bottleneck parts of the firstprinciples transport calculation. Over the past years, several methods have been developed to reduce the computational cost, however calculation is still slow especially when the realspace pseudopotential method is employed because the Hamiltonian matrix of the unit cell becomes very large. 
Thursday, March 7, 2019 4:42PM  4:54PM 
V18.00012: On the δfunction broadening in KuboGreenwood equation Pavlo Bulanchuk We propose a solution to a longstanding issue in the calculation of KuboGreenwood DC conductivity in finitesized quantum systems. The KuboGreenwood equation contains a sum of deltafunctions, which are usually broadened. The estimate of the DC conductivity depends significantly on the type of broadening applied, making the estimate ambiguous. We eliminate the ambiguity by mapping the broadening onto a specific way of introduction of the electric field and making a correction based on Drude equation. We also consider the influence of deltafunction broadening on conductivity averaged over disorder. We demonstrate the influence can be reduced to a convolution of the average conductivity with the broadening function over the frequency. Even though in finite systems the average conductivity is an oscillatory function of frequency, if convolved with a slowly varying function, it behaves similarly to a Lorentzian. We propose a procedure of extracting the parameters of the Lorentzian by extrapolation similarly to a single system. 
Thursday, March 7, 2019 4:54PM  5:06PM 
V18.00013: Minimizing Reflections in Electronic Structure Calculations Gregory Benesh, Roger Haydock In electronic structure calculations, large aggregates of atoms are usually approximated by model systems containing far fewer atoms—introducing artificial boundaries that do not occur in the original system. These boundaries ordinarily produce reflected waves that interfere with outgoing solutions of the Schrödinger equation. Depending on the degree of interference, computational results from model calculations may differ widely from the characteristics of the real physical system. Examples of computational studies exhibiting such interference effects abound in many areas of physics. One approach to eliminating the reflection problem is to choose Schrödinger solutions that minimally reflect at the artificial boundary of the model system. These socalled Maximum Breaking of TimeReversal Symmetry (MBTS) solutions come in pairs that maximally carry current in opposite directions. In effect, by using MBTS solutions, the boundary becomes transparent or nearlytransparent to traveling waves. The MBTS formalism and results for several model systems will be presented. 
Thursday, March 7, 2019 5:06PM  5:18PM 
V18.00014: Longwavelength densityfunctional perturbation theory Massimiliano Stengel Densityfunctional perturbation theory (DFPT) is nowadays the method of choice for the accurate computation of linear and nonlinear response properties of materials from first principles. A notable advantage of DFPT over alternative approaches is the possibility of treating incommensurate lattice distortions with an arbitrary wavevector, q, at comparable computational cost as the latticeperiodic case. 
Thursday, March 7, 2019 5:18PM  5:30PM 
V18.00015: WITHDRAWN ABSTRACT

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