Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session R19: Density Functional Theory and Beyond IIILive

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Sponsoring Units: DCOMP DCP DCMP DPOLY Chair: Koblar Jackson, Central Michigan Univ 
Thursday, March 18, 2021 8:00AM  8:12AM Live 
R19.00001: Analyticity with respect to external potential in DFT and implications for KohnSham computation Paul Lammert

Thursday, March 18, 2021 8:12AM  8:24AM Live 
R19.00002: Density Functional Theory Study of the Optical and Electronic Properties of WithDefect Semiconductors using a Tuned Screened RangeSeparated Hybrid Kirk Lewis, Ashwin Ramasubramaniam, Sahar Sharifzadeh Tuned and screened rangeseparated hybrid (SRSH) methods have emerged as an alternative to state of the art manybody perturbation theory (MBPT) calculations of the optoelectronic properties of materials. Specifically, it has been shown that SRSH hybrid methods can approach the quantitative accuracy of MBPT at the cost of hybrid DFT for a variety of dissimilar molecules and both bulk and monolayer crystals. Here, we test the accuracy of the timedependent (TD) SRSH approach for describing the optoelectronic properties of defective semiconductors by the study of point defects in bulk GaN. We first show that the predicted quasiparticle gap and lowenergy excitation spectra of (TD)SRSH and GW/BSE agree well in both pristine GaN and GaN with a single nitrogen vacancy, establishing the accuracy of the method. Aided by the reduced computational cost of (TD)SRSH, we then report on a series of technologically relevant point defects and complexes in GaN. This study indicates that TDSRSH is a promising and computationally feasible approach for quantitatively accurate, firstprinciples modeling of defective semiconductors. 
Thursday, March 18, 2021 8:24AM  8:36AM Live 
R19.00003: Accurately predicting electron affinities with Koopmans spectral functionals Edward Linscott, Nicola Colonna, Riccardo De Gennaro, Nicola Marzari Density functional theory (DFT) is a popular method for electronicstructure calculations. But while KohnSham eigenvalues can loosely mirror experimental quasiparticle energies, there is formally no connection between the two (except for the HOMO in exact DFT). Furthermore, the presence of selfinteraction errors in semilocal DFT can make those eigenvalues an even poorer proxy for quasiparticle energies [1]. 
Thursday, March 18, 2021 8:36AM  8:48AM Live 
R19.00004: Optical absorption spectra from model exchangecorrelation (XC) kernels SANTOSH NEUPANE, Niraj K Nepal, Adrienn Ruzsinszky We use model exchangecorrelation (XC) kernels in the framework of time dependent density functional theory (TDDFT) to obtain the optical absorption spectra of different bulk materials. We also calculate the optical absorption spectra by solving the BetheSalpeter equation (BSE) for the twoparticle Green’s function. We test various kernels such as JGM and JGMG [1] on different bulk materials, and compare them with the Random Phase Approximation (RPA). In addition, we compare all the results with the experimental spectra when available. We find that model xc kernels built upon exact physical constraints are reasonably accurate for the optical response properties of bulk solids. 
Thursday, March 18, 2021 8:48AM  9:00AM Live 
R19.00005: Bandgap of bulk solids and twodimensional bent nanoribbons from firstprinciples Bimal Neupane, Hong Tang, Niraj K Nepal, Adrienn Ruzsinszky

Thursday, March 18, 2021 9:00AM  9:12AM Live 
R19.00006: Barrier Heights of BH76 Database with PZSIC and Locallyscaled Self Interaction Correction Methods Prakash Mishra, Yoh Yamamoto, Koblar Jackson, Tunna Baruah, Rajendra R Zope We investigate the performance of the PerdewZunger (PZ) selfinteraction correction (SIC) method and recent locally scaled SIC (LSIC) method[1] for predicting barrier heights in chemical reactions using the BH76 database. Selfinteraction error (SIE) is pronounced when molecules or solids are not in equilibrium, such as when chemical bonds are stretched or broken during chemical reactions. We determine the SIC using FermiLöwdin orbitals[2]. We find that removing SIE using the PZSIC energy functional in the FLOSIC framework reduces the overall errors, but in PZSICLSDA the barriers are still too small compared to reference values. Applying LSICLSDA improves the barrier heights in almost every case resulting in better agreement with experiment and the accurate reference values from the higherlevel calculations. 
Thursday, March 18, 2021 9:12AM  9:24AM Live 
R19.00007: Quantifying and reducing different sources of errors in DFT calculations Stefan Vuckovic, Suhwan Song, Eunji Sim, Kieron Burke Density functional theory (DFT) calculations are ubiquitous in different branches of chemistry and physics. While in principle, DFT is an exact theory, in practice, it must rely on approximations. In this talk, I will describe a set of approaches for disentangling different sources of errors in approximate DFT calculations. I will discuss how errors in approximate molecular geometries [1] and approximate electronic densities [2–4] affect the overall accuracy of DFT calculations. Then I will explain how these insights can be used to improve the performance and to reduce the cost of DFT calculations with implications for both molecules and surfaces. 
Thursday, March 18, 2021 9:24AM  9:36AM Live 
R19.00008: Density sensitive analysis for evaluating density functional theory approximations to exchangecorrelation energies Ryan J. McCarty, Stefan Vuckovic, Suhwan Song, John Kozlowski, Eunji Sim, Kieron Burke We developed a density sensitivity difference measure using theory from densitycorrected Density Functional Theory that provides a physicallymotivated comparison of exchangecorrelation functional approximations. Analyzing the comparative density sensitivities with machinelearning reveals striking trends among standard functionals. Comparative differences between approximate functionals are more easily quantified than absolute errors, and are indifferent to the intent or construction of the functional. Evaluating individual molecules with this approach indicates clear molecular groupings, highlighting the similarities or differences of various external potentials. Our analysis provides a new method for evaluating DFT functionals, and enables a new data driven approach for dataset generation. 
Thursday, March 18, 2021 9:36AM  9:48AM Live 
R19.00009: Accelerating the FermiLöwdin Orbital Descriptor Optimizations for SelfInteraction Free Density Functional Theory Calculations. Md Nageeb Bin Zaman, Koblar Alan Jackson, Juan Ernesto Peralta The FermiLöwdin Self Interaction Correction (FLOSIC) method was introduced to address the shortcomings of standard density functional approximation calculations by removing the spurious electron selfinteraction [14]. Within this method, a set of Fermi orbital descriptors (FODs) need to be optimized to minimize the energy. Current FOD optimization algorithms require large numbers of steps and the number of steps grows with systems size, that is, as the number of FODs increases. Moreover, every step in this optimization process requires the timeconsuming evaluation of singleparticle potential energy functions. Here we propose a strategy to reduce the number of single particle potential evaluations, making the FOD optimization step in FLOSIC calculations more efficient. We will present proofofconcept results for small molecules and compare with existing optimization schemes. 
Thursday, March 18, 2021 9:48AM  10:00AM Live 
R19.00010: A new method for initializing Fermi orbital descriptors for FLOSIC calculations Duyen Nguyen, Koblar Alan Jackson, John Perdew, Mark Pederson, Juan Ernesto Peralta Fermi orbital descriptors (FODs) play a key role in FermiLöwdin orbital selfinteraction correction (FLOSIC) calculations used to remove oneelectron selfinteraction from approximate density functional calculations on an orbitalbyorbital basis. Optimal FODs are obtaining by minimizing the SIC energy, and, in this process, identifying an initial set of FODs becomes crucial for practical applications. Here we propose a novel generator for automatically initializing FODs without requiring much user input based on the minimization of a “pseudo energy” expression that involves a Coulomb electron density attraction, a FODFOD shortrange repulsion, and an exchangelike density repulsion term. We implemented and tested this method for molecules involving a variety of bonding situations and found that it successfully reproduces FOD configurations that are in qualitative good agreement with Lewis theory. For spinunpolarized molecules, this method underestimates and overestimates the separation of lone pair FODs in the second and thirdrow elements, respectively, while the distances between double and triple bond FODs are slightly exaggerated. For spinpolarized systems, this method can also provide good FODs for radicals and transition states. 
Thursday, March 18, 2021 10:00AM  10:12AM Live 
R19.00011: Fragment Electron Populations in Partition Density Functional Theory Kui Zhang, Adam Wasserman Partition Density Functional Theory (PDFT) is a densitybased embedding method that partitions a system into fragments by minimizing the sum of fragment energies subject to two constraints: (1) That the sum of fragment densities equals the density of the system; (2) That the sum of fragment electron populations equals the total number of electrons. To perform this constrained minimization, we study a twostage procedure in which the sum of fragment energies is lowered when electrons flow from fragments of lower electronegativity to fragments of higher electronegativity. The global minimum is reached when all electronegativities are equal. The nonintegral fragment electron populations are dealt with in two different ways: (1) by using fractionally occupied orbitals (FOO) and (2) ensemble (ENS) treatments. Although these two methods lead to the same total energy and density, they lead to different fragment properties and partial charges. We compare exact PDFT calculations with results obtained from the LocalDensity Approximation (LDA) for heteronuclear diatomic molecules. We find that the electron numbers transferred in ENS are generally smaller than that in FOO, and explain why. 
Thursday, March 18, 2021 10:12AM  10:24AM Live 
R19.00012: Unharmonic adiabatic potential by shortrange correlation effect enlarging C_{33} of crystalline graphite Koichi Kusakabe, Akira Nagakubo, Hirotsugu Ogi, Kensuke Murashima, Mutsuaki Murakami In our previous work using the LDA+U+RPA method [1], we reported a theoretical value of C_{33} of graphite as large as 48GPa when cRPA estimation of the onsite U for 2porbitals is used. Renormalization in Wannier functions determined at each point on the adiabatic potential surface is essential. Fixed localized orbital cannot cause the enhancement of C_{33} from a value by ACFDTRPA, which is more than 20% smaller than the observed C_{33} of defectfree monocrystalline graphite. In this presentation, after discussing relevance of the multireference extension of DFT[2] for beyondRPA approaches, we open comparison among several +U approaches with the doublecounting term. 
Thursday, March 18, 2021 10:24AM  10:36AM Live 
R19.00013: Efficient FirstPrinciples Approach with a Pseudohybrid Density Functional for Extended Hubbard Interactions SangHoon Lee, YoungWoo Son For massive databasedriven materials research, there are increasing demands for both fast and accurate quantum mechanical computational tools. Contemporary density functional theory (DFT) methods can be fast sacrificing their accuracy or be precise consuming a significant amount of resources. Here, to overcome such a problem, we present a DFT method that exploits selfconsistent determinations of the onsite and intersite Hubbard interactions (U and V ) simultaneously and obtain band gaps of diverse materials in the accuracy of GW method at a standard DFT computational cost. To achieve selfconsistent evaluation of U and V , we adapt a recently proposed AgapitoCurtaroloBuongiorno Nardelli pseudohybrid functional for U to implement a new density functional of V . This method is found to be appropriate for considering various interactions such as local Coulomb repulsion, covalent hybridization and their coexistence. We also obtained good agreements between computed and measured band gaps of low dimensional systems, thus meriting the new approach for largescale as well as high throughput calculations for various bulk and nanoscale materials with higher accuracy. 
Thursday, March 18, 2021 10:36AM  10:48AM Live 
R19.00014: ReverseEngineering the ExchangeCorrelation hole for the SCAN and r^{2}SCAN Functional Luis Lopez Macias, John Perdew, Jianwei Sun The success of density functional theory (DFT) of electronic structure is dependent on the development of accurate and efficient density functional approximations (DFAs). These DFAs are limited by the approximation of its exchangecorrelation (XC) energy which can be defined by the XC hole. Understanding this XC hole has played a vital role developing DFAs and explaining their success and limitations. We present a construction of the XC hole model for SCAN [1] and the recent r^{2}SCAN [2] by reverse engineering from known exact hole constraints. The hole models are tested for atoms and simple molecules. 
Thursday, March 18, 2021 10:48AM  11:00AM Live 
R19.00015: BeyondDFT database of spectral function for correlated materials Subhasish Mandal, Kristjan Haule, Karin M Rabe, David Vanderbilt Recent trends in condensed matter physics greatly rely on the database and data sciencedriven materials discovery. The existing materials databases, constructed in the spirit of the materials genome initiative, are built almost exclusively by DFT engines and are very often making incorrect predictions for many correlated materials. As for qualitative predictions of excitedstate properties usually require beyondDFT methods, various methods going beyond DFT, such as metaGGAs, hybrid functionals, GW, & DMFT have been developed to describe the electronic structure of correlated materials, but it is unclear how accurate these methods can be expected to be when applied to a given material. It is thus of pressing interest to compare their accuracy as they apply to different categories of materials, and at the same time, to build up a database for beyondDFT methods [1]. We discuss a systematic study of these methods on various training sets of moderately and strongly correlated materials starting from elemental metallic systems to Fepnictides and chalcogenides, and various perovskites and compare with experimental photoemission data where available. 
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