Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T01: Density Functional Theory and Beyond VIFocus Recordings Available

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Sponsoring Units: DCP Chair: Adam Wasserman, Purdue Room: McCormick Place W175A 
Thursday, March 17, 2022 11:30AM  12:06PM 
T01.00001: What does it take to run orbitalfree (TD)DFT and embedding simulations? And what do we get from them? Invited Speaker: Michele Pavanello This talk discusses orbitalfree DFT and DFT embedding methods. Both rely on pure density functionals for the noninteracting kinetic energy, exchange and correlation. When venturing to nonequilibrium processes, semiquantitative to quantitative agreement with reality can only be achieved if nonadiabaticity and nonlocality is accounted for. Upon inclusion of nonlocality, embedding simulations reach a subkcal/mol accuracy in the intersubsystem interactions dramatically widening the applicability of DFT to large system sizes. When nonadiabaticity is included in the Pauli potential, orbitalfree TDDFT can be used to compute optical spectra and electron dynamics of metal and semiconductor systems with confidence in the usefulness of the results. The talk also touches upon best practices to realize efficient computer software encoding DFT embedding and orbitalfree (TD)DFT and how to train the next generation of DFT software developers. 
Thursday, March 17, 2022 12:06PM  12:18PM 
T01.00002: Nonlocal and Nonadiabatic Timedependent Pauli Potential Kaili Jiang, Xuecheng Shao, Michele Pavanello Timedependent orbitalfree density functional theory (TDOFDFT) is an efficient abinitio method for calculating the electronic dynamics of large systems. In comparison to standard TDDFT, it computes only a single electronic state regardless of system size, but it requires an additional timedependent Pauli potential term. Based on the frequencydependent Pauli kernel of the free electron gas, we propose a nonadiabatic and nonlocal Pauli potential as a functional of the timedependent particle and current densities. Our calculations of the optical spectra of metallic and semiconductor clusters indicate that nonlocal and nonadiabatic TDOFDFT performs accurately for metallic systems and semiquantitatively for semiconductors. This work opens the door to wide applicability of TDOFDFT for nonequilibrium electron and electronnuclear dynamics of materials. 
Thursday, March 17, 2022 12:18PM  12:30PM 
T01.00003: Investigation of cusps and steps in the nonadditive kinetic potential functional V^{nad }from analytic inversion Tim Gould, Leeor Kronik, David A Strubbe, Mojdeh Banafsheh The nonadditive kinetic potential functional V^{nad} is a key issue in densitydependent embedding methods, such as Frozen Density Embedding Theory and PartitionDFT. V^{nad} is a bifunctional of pair of electron densities ρ_{A} and ρ_{B}. We previously reported the exact analytical inversion procedure to generate reference V^{nad} for weakly overlapping ρ_{A} and ρ_{B}(M. Banafsheh, T. A. Wesolowski, Int. J. Quant. Chem. 118 (2018): e25410). The behaviour of V^{nad} at the vicinity of the nuclei has been questioned since the beginning. Available computational tools and methods in the past led to a cusp at nuclei in V^{nad }calculations. We analyse existence and nonexistence properties of the cusp in V^{nad} analytically, and compare against nuclear cusps condition for the groundstate density and resulting cusp in the KohnSham potential. We show the agreement of numerical calculations with this fact for various diatomic model systems of two and four electrons. The results are compared to the von Weizsäcker functional (exact for one orbital) and other kinetic energy functionals. 
Thursday, March 17, 2022 12:30PM  12:42PM 
T01.00004: Consistent deorbitalization and new deorbitalizers for metaGGA exchangecorrelation functionals Hector I Francisco Rodriguez, Samuel B Trickey, Antonio C Cancio A key challenge for use of KohnSham density functional theory is to improve the quality and accuracy of lowcomputational cost exchangecorrelation (XC) density functional approximations (DFAs). Deorbitalization, the replacement of the KS kinetic energy density in a metaGGA with an explicit function of n(r), its gradient, and its laplacian, is a recently successful approach with the SCAN and r^{2}SCAN DFAs [Phys. Rev. A 96, 052512 (2017); Phys. Rev. B 102, 121109 (2020)]. Their procedure was not entirely consistent. Here we reparametrize the α switching function consistently with the atomic densities of the parent DFAs. The result is almost indistinguishable from the original: slight improvements on heats of formation (G3/99X), bond lengths (T96R), and vibration frequencies (T82F). We also have extended consistent deorbitalization to the original, regularized, and revised regularized TaoMo DFAs [Phys. Rev. Letter. 117, 073001 (2016); J. Chem. Phys. 153, 184112 (2020); J. Chem. Phys. 155, 024103 (2021)] with good results. 
Thursday, March 17, 2022 12:42PM  12:54PM 
T01.00005: TwoOrbital Approximation for Partition Density Functional Theory Victor Hugo Gonzalez Chavez, Yan Oueis, Adam Wasserman Partition Density Functional Theory (PDFT) is an embedding method in which molecular properties are computed through calculations on the molecule’s constituents. The lack of an accurate approximation for the noninteracting kinetic energy functional in terms of the set of fragment densities makes practical PDFT calculations a challenge. We have shown that a simple expression for the nonadditive kinetic energy based on a “twoorbital approximation” (2OA) reproduces extremely well the largeR asymptotic behavior of the dissociation energy of raregas dimers with internuclear separation R. We discuss here the physical motivation behind the construction of the 2OA, its limitations, and how we are extending it to make it more applicable to a broader class of molecules. 
Thursday, March 17, 2022 12:54PM  1:06PM 
T01.00006: Deriving Corrections to the 1D TF Kinetic Energy Functional: The first step towards a systematic DFT Pavel Okun, Kieron Burke Recent developments have shown that density functionals can be derived from semiclassical quantum mechanics in a systematic fashion reminiscent of wavefunction electronic structure. This new technique is completely different from other approaches to functional design (such as the satisfaction of exact conditions or fitting empirical parameters). The ThomasFermi kinetic energy functional, which Lieb and Simon showed is exact in the semiclassical limit, is the lowest order term in a semiclassical expansion of the exact kinetic energy functional. We will show, at least in one dimension, how higher order corrections to this series can be obtained by calculating the sums of eigenvalues and then inverting these sums into density functionals. Thus we show how to generate the exact asymptotic expansion of the true kinetic energy functional. We will also demonstrate that boundary terms arise from the turning points/surfaces where the density cannot be slowly varying, which are missed by the traditional gradient expansion. To simplify our analysis we have worked in 1D but we shall comment on the application of our work to real electronic systems and show some preliminary results on simple 3D systems. 
Thursday, March 17, 2022 1:06PM  1:18PM 
T01.00007: Suppressing exchangecorrelation errors through a Generalized Overlap Approximation in PartitionDFT Yuming Shi, Adam Wasserman Quantum embedding methods can in principle lead to linear scaling and multilevelaccuracy calculations of electronic properties of molecules and materials. Partition Density Function Theory (PDFT), a densitybased embedding method, features a unique interaction potential and in many cases fragments with fractional numbers of electrons. An "overlap approximation" (OA) for the partition energy of PDFT has been shown to eliminate errors caused by the underlying exchangecorrelation approximations, such as delocalization and staticcorrelation errors, even when using the Local Density Approximation for the fragments. Although the initial formulation of the OA was applicable only to small homonuclear diatomic molecules, we have revised its derivation and demonstrated its applicability to larger, less symmetric systems. 
Thursday, March 17, 2022 1:18PM  1:30PM 
T01.00008: Visualizing and testing orbital free models of the kinetic energy density in semiconductors Antonio C Cancio, Akinfolarin Akinola, Brielle Shope

Thursday, March 17, 2022 1:30PM  1:42PM 
T01.00009: Variational optimization of Pauli potentials for orbitalfree density functional theory Antonio C Cancio, Bishal Thapa The goal of OrbitalFree Density Functional Theory is to model the KohnSham noninteracting kinetic energy as a functional of ingredients derived from the density directly, so as to remove the bottleneck of computing orbitals in large systems. The PerdewConstantin KE metaGGA [1] and later improvements [2] use the Laplacian of the density to switch from the slowly varying electron gas to the von Weizsacker or single electronpair limits. While producing an accurate KE density, that use of the density Laplacian creates unphysically spiky Pauli potentials that are numerically difficult to solve and lead to noisy results. To ameliorate this problem, we construct and test a smoothness measure based on the variational description of Poisson's equation, applied to the Laplaciangenerated terms in the potential. Optimization of PClike models with respect to this measure under the constraint of preserving the total kinetic energy can substantially but not completely remove unphysical features in the Pauli potentials of small atoms. We discuss prospects for using the result in deorbitalized metaGGA functionals. 
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