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 X21: Density Functional Theory and Beyond IVLive
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Sponsoring Units: DCOMP DCP DCMP DPOLY Chair: Rajendra Zope, University of Texas, El Paso |
Friday, March 19, 2021 8:00AM - 8:12AM Live |
X21.00001: Constraint-based wave vector and frequency-dependent exchange-correlation kernel of the uniform electron gas Adrienn Ruzsinszky, Niraj K Nepal, Jose M. Pitarke, John Perdew The accuracy of time-dependent density functional theory (TDDFT) is restricted by the limitations of the exchange-correlation kernels that are commonly in use. In addition to frequency-dependence a sophisticated spatial nonlocality of the kernel is also required. In this work a dynamic model exchange-correlation kernel, the MCP07 based on exact constraints is introduced [1]. For the static limit, we modified the model of CP07 at small wavevector q to recover the known second-order gradient expansion, plus other changes. For the zero-wavevector limit, we use the frequency-dependent Gross-Kohn kernel. The dynamic MCP07 exchange-correlation kernel predicts a static charge-density wave at low densities and delivers excellent quality correlation energies for the ground state, while it predicts a plausible finite plasmon lifetime at all wavevectors for the first time within TDDFT. We aim to make TDDFT more applicable to challenging physical situations by exploiting these attractive features of the dynamic MCP07 kernel. |
Friday, March 19, 2021 8:12AM - 8:24AM Live |
X21.00002: Local scaled self-interaction-correction method using Fermi-Löwdin orbitals and a simple scaling factor Selim Romero, Yoh Yamamoto, Tunna Baruah, Rajendra R Zope A recently proposed local self-interaction correction (LSIC) method[1] when applied to the simplest local density approximation provides significant improvement over standard Perdew-Zunger SIC (PZSIC) for both equilibrium properties such as total or atomization energies as well as properties involving stretched bond such as barrier heights. The method uses an iso-orbital indicator to identify the single-electron regions. In this talk, we present the performance of the LSIC method using a simpler scaling factor was a ratio of orbital and spin densities in place of the ratio of kinetic energy densities z. Our study shows that the present LSIC(w) performance is comparable to LSIC(z) for most properties but on average has slightly larger errors than LSIC(z). For the binding energies of weakly hydrogen bonded water clusters, however, LSIC(w) performs significantly better than LSIC(z) which provides poor description of weakly bonded systems. |
Friday, March 19, 2021 8:24AM - 8:36AM Live |
X21.00003: Analyzing the Large Z Exchange Expansion Jeremy Redd, Antonio C Cancio Lieb-Simon zeta-scaling, which describes the scaling of neutral closed-shell atoms as Z approaches infinity, has been used with marked success to provide theoretical constraints on density functionals. Because the electronic core of an atom as the nuclear charge approaches infinity relatively approaches a homogeneous electron gas (HEG), energy data for large Z atoms can be used to probe perturbative corrections to density functionals. The exact large Z expansion about a HEG for the exchange energy has never been explicitly calculated beyond the leading order Z5/3 term. It is typically assumed that the next order term is of order Z. We calculate exact exchange energies using the Optimized Effective Potential (OEP) method for closed-shell atoms up to Z=120 and other standard DFT models up to 976. Regression analysis shows that LDA exchange has a second-order term of order Z4/3, and support a similar behavior for GGA’s. Exchange may also have a small contribution of order ZlogZ. Due to the high agreement between OEP and Becke 1988 exchange, we suspect this will be true of exact exchange as well. This may lead to improved constraint information to develop more robust exchange functionals. |
Friday, March 19, 2021 8:36AM - 8:48AM Live |
X21.00004: Local modified Becke-Johnson potential for low-dimensional systems Tomas Rauch, Miguel Marques, Silvana Botti We propose an extension to the modified Becke-Johnson potential [1] that enables its use to study both heterogeneous and low-dimensional systems [2]. This is achieved by using a coordinate-dependent expression for the c parameter, in contrast to the original global formulation. Our functional builds on the excellent description of bulk band gaps of the modified Becke-Johnson potential and preserves its modest computational effort. Furthermore, it yields with one single calculation band-diagrams and band-offsets of heterostructures, interfaces, and surfaces. We exemplify the usefulness and efficiency of our local functional by testing it for a series of semiconductor interfaces, surfaces, two-dimensional systems [3,4], and molecules. |
Friday, March 19, 2021 8:48AM - 9:00AM Live |
X21.00005: Conditional probability density functional theory Ryan J. McCarty, Dennis R Perchak, Ryan Pederson, Robert Evans, Yiheng Qiu, Steven Robert White, Kieron Burke We present conditional probability (CP) density functional theory (DFT) as a formally exact theory. In essence, CP-DFT determines the ground-state energy of a system by finding the CP density from a sequence of Kohn-Sham (KS) calculations. Unlike standard KS-DFT, which relies on an accurate exchange-correlation (XC) functional to extract energies, CP-DFT only requires accurate self-consistent densities. A simple CP-DFT approximation yields usefully accurate results for two-electron ions and the hydrogen dimer. CP-DFT has no self-interaction error for one electron, and correctly dissociates H2, both major challenges in standard KS-DFT. |
Friday, March 19, 2021 9:00AM - 9:12AM Live |
X21.00006: Bulk properties of semiconductors calculated with density functional theory and screened range-separated hybrids Stefan Seidl, Bernhard Kretz, Christian Gehrmann, David Egger While well-established semilocal and hybrid functionals commonly used in density functional theory (DFT) perform well for predicting structural properties, they fail quantitatively when it comes to the description of optical and electronic-structure properties. A promising alternative to conventional hybrids are screened range-separated hybrid (SRSH) functionals, which have recently been proven to yield high-precision electronic-structure and optical properties of prototypical semiconductors [1]. The SRSH approach uses a single empirical parameter, where the range separation is tuned in such a way that SRSH reproduces the GW band gap [1]. Here, we evaluate the accuracy of the SRSH approach for computing bulk properties (e.g., lattice constants, bulk moduli, atomization energies) and phonon dispersion relations of several prototypical semiconductors. For this purpose, we compare the results of the SRSH method to experimental data and to results obtained by conventional semilocal and hybrid DFT functionals. |
Friday, March 19, 2021 9:12AM - 9:24AM Live |
X21.00007: On the relationship between the Kohn-Sham potential, the Pauli potential, and the Exact Electron Factorization Axel Schild, Jakub Kocák, Eli Kraisler The EEF is an exact one-electron theory of a many-electron problem where many-electron effects are described by a potential v in a one-electron Schrödinger equation. This equation is identical to the central equation of Orbital-Free DFT. However, the constructions of v are very different: OF-DFT typically relies on Kohn-Sham DFT and separates v into KS-potential and Pauli potential. In the EEF, v is a sum of physically transparent terms. A particular advantage of the EEF formalism is that it provides explicit equations for the components of v in terms of the many-electron wavefunction, which are neither available for KS-DFT nor for OF-DFT. |
Friday, March 19, 2021 9:24AM - 9:36AM Live |
X21.00008: A simple self-interaction correction to the RPA+ correlation energy Shiqi Ruan, Xinguo Ren, Tim Gould, Adrienn Ruzsinszky The exchange energy of Random Phase Approximation is exact for a many-body ground state, but the correlation energy is often overestimated in magnitude. This error comes from a poor description of the short-range correlation. RPA+ largely reduces the error by adding a local or semi-local correction [1]. RPA+, on the other hand, is accurate for the total energies of atoms and binding energies. However, RPA+ fails to provide much improvement over RPA for single-election systems like the stretched H2+ and systems where spin-polarization plays a significant role such as atomization energies. Within this work, we have introduced a simple correction to the RPA+ correlation energy (mgRPA+) to make it exact for a single-electron system [2,3]. We then investigated how this approximation works for atomization energies, ionization energies, electron affinities and the dissociation of H2+ and He2+. We found that with little extra computational cost mgRPA+ outperforms RPA+ in all the tests we have considered. |
Friday, March 19, 2021 9:36AM - 9:48AM Live |
X21.00009: Improving density functional calculations of molecular polarizabilities using locally
scaled self-interaction corrections. Kamal Sharkas, Sharmin Akter, Jorge A Vargas, Juan Ernesto Peralta, Koblar Alan Jackson, Tunna Baruah, Rajendra R Zope The molecular polarizability characterizes the first response of the electronic charge of a molecule placed in a static electric field. From the computational viewpoint, the static polarizabilities are important for predicting intermolecular interactions. In the Kohn–Sham density functional theory (KS–DFT), present day functionals are known to overestimate the molecular polarizabilities. Using a recent benchmark static polarizabilities database, we examine the effect of self-interaction errors (SIE) in the molecular polarizabilities at the level of the local density approximation (LSDA). Our results shows that the Perdew-Zunger scheme with Fermi-LÖwdin orbital self-interaction correction (FLOSIC)1 methodology leads to underestimated polarizabilities due to overcorrections. However, employing the strategy of scaling down the SI correction term in the recently developed local-scaling self-interaction correction (LSIC)2 will result in excellent agreement with the benchmarked values of static polarizabilities. |
Friday, March 19, 2021 9:48AM - 10:00AM Live |
X21.00010: Effect of the oxygen coverage on the electronic and magnetic properties of Cr2N MXene Rodrigo Ponce Perez, María Guadalupe Moreno Armenta, Jonathan Guerrero Sanchez We use DFT calculations to investigate the electronic and magnetic properties of Cr2N MXene functionalized by oxygen at different coverages. Results show that oxygen adsorption happens at the H3 site. Pristine Cr2N exhibits metallic and AFM characteristics. FM Cr oxide islands are obtained at 1/8 ML, become the system semiconductor. For ¼ and ½ ML the system is AFM, in both cases the material is half-metal. At 5/8 and ¾ ML coverages the material remains AFM, however, the material becomes semiconductor. For 7/8 ML AFM and FM configurations are degenerated, the AFM case is semiconductor and the FM is half-metal. For a coverage of 1ML the system becomes FM with half-metal characteristics. We show an effective way to tune the electronic properties of Cr2N modifying the O coverage, laying the foundations to use these materials in the spintronics industry. |
Friday, March 19, 2021 10:00AM - 10:12AM Live |
X21.00011: Surface structures of magnetostrictive D03-Fe3Ga(001) Ricardo Ruvalcaba, Joseph Perry Corbett, Andrada-Oana Mandru, Noboru Takeuchi, Arthur Smith, Jonathan Guerrero Sanchez First-principles total energy calculations and STM experiments were performed to study the surface reconstruction on the magnetostrictive Fe3Ga alloy. The inverse magnetostrictive behavior was evaluated in the bulk by varying its lattice parameter. Surface analysis demonstrates two thermodynamically stable surfaces, the ideal FeGa-terminated 1×1 and the Ga-substituted 3×1. The latter forms row-like surface structures. Tersoff–Hamann STM simulations were obtained and found excellent agreement with the experiment, in which the distance between rows is ~12.3 Å. Analysis of the magnetic moments in the reconstructions showed that their behavior is affected by a surface effect, as well as by the inverse magnetostriction of the structure. |
Friday, March 19, 2021 10:12AM - 10:24AM Live |
X21.00012: Interpretations of ground-state symmetry breaking and strong correlation in wavefunction and density functional theories John Perdew, Adrienn Ruzsinszky, Jianwei Sun, Niraj K Nepal, Aaron Kaplan Strong correlations within a symmetry-unbroken ground-state wavefunction can show up in approximate density functional theory as symmetry-broken spin-densities or total densities. They can arise from soft modes of fluctuations (sometimes collective excitations) such as spin-density or charge density waves at non-zero wavevector. Familiar examples are the unobservable but revealing symmetry breaking in stretched H2 and the observable symmetry breaking in antiferromagnetic solids. The example discussed here is the static charge-density wave/Wigner crystal phase of a low density ( rs = 69) jellium. Time-dependent density functional theory is used to show quantitatively that the static charge density wave is a soft plasmon. More precisely, the frequency of a related density fluctuation drops to zero, as found from the frequency moments of the spectral function. Our calculation is based on a recent constraint-based wavevector- and frequency-dependent jellium exchange-correlation kernel.1 |
Friday, March 19, 2021 10:24AM - 10:36AM Live |
X21.00013: Constrained Machine Learning de-orbitalization of meta-GGA exchange-correlation functionals Kanun Pokharel, James Furness, Yi Yao, Volker Blum, Jianwei Sun The Strongly Constrained and Appropriately Normed (SCAN) density functional, which has shown impressive performance for diverse problems [1], takes the orbital kinetic energy density τ(r) as an ingredient in its construction. While theoretically convenient, the orbital dependence of τ(r) complicates the exchange-correlation potential and increases computational cost. Recently, Rodriguez and Trickey used the density Laplacian ▽2n(r) to produce a “de-orbitalized” SCAN, without significantly degrading accuracy [2]. This suggests an intriguing but unclear relationship between τ(r) and ▽2n(r). We use deep neural network to construct a machine learned functional model that exploits this relationship to de-orbitalize SCAN (SCAN_ML) and augment it with by enforcing simple exact constraints on the model’s output. The performance and transferability of the machine learned functional is established for molecular and periodic systems. |
Friday, March 19, 2021 10:36AM - 10:48AM Live |
X21.00014: Removing Combinatorial Complexity for Systematic Initialization of Electronic Geometries for Fermi-Löwdin-Orbital Self-Interaction Corrections to Density Functional Approximations Chandra Shahi, Koblar Alan Jackson, Mark Pederson Density functional theory suffers from the self-interaction error due to the approximation of the exchange-correlation energy. The Fermi-Löwdin-Orbital (FLO) self-interaction correction (SIC) [1] employs the Perdew-Zunger (PZ) theory [2] in which the PZ SIC energy is minimized with respect to the Fermi orbital descriptors (FODs). FODs are the positions in space where FLOs are localized and are the ingredients needed to define a unitary transformation that connects localized and canonical orbitals. They can be viewed as describing a quasi-classical electronic geometry. In the FLO-SIC method, a major challenge is the initialization of the FOD geometry for systems containing transition metal ions and for systems having double or resonance bonds. We describe a machine-human learning paradigm that reduces the combinatorial complexity associated with initiating FODs to a hierarchical screening approach that reduces the search to a series of single-atom calculations. Examples of this approach to several difficult systems, including a trianionic molecule with a magnetically active center, will be discussed. |
Friday, March 19, 2021 10:48AM - 11:00AM Live |
X21.00015: Scaling down the Perdew-Zunger self-interaction correction to the first three rungs of the ladder of density functional approximations Biswajit Santra, Puskar Bhattarai, Kamal Wagle, Chandra Shahi, Yoh Yamamoto, Selim Romero, Rajendra R Zope, Juan E Peralta, Koblar Jackson, John Perdew The Perdew–Zunger (PZ) self-interaction correction (SIC) was designed to correct the one-electron limit of any approximate density functional for the exchange-correlation (xc) energy, while yielding no correction to the exact functional. However, it spoils the slowly varying (in space) limits of the uncorrected approximate functionals, where those functionals are correct by construction. The right limits can be restored by locally scaling down the energy density of the PZ SIC in many-electron regions, but then a spurious correction to the exact functional would be found unless the self-Hartree and exact self-xc terms of the PZ SIC energy density are expressed in the same gauge. A transformation1 of energy density that achieves the Hartree gauge for the exact xc functional can also be applied to approximate functionals. Doing so leads to a simple scaled-down SIC that is typically much more accurate than PZ SIC in tests for many molecular properties (including equilibrium bond lengths). The present work unambiguously shows that the largest errors of PZ SIC applied to standard functionals at three levels of approximation can be removed by restoring their correct slowly-varying density limits. |
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