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 C19: Density Functional Theory and Beyond ILive

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Sponsoring Units: DCOMP DCP DCMP DPOLY Chair: James Furness, Tulane Univ 
Monday, March 15, 2021 3:00PM  3:12PM Live 
C19.00001: A spectral scheme for KohnSham Density Functional Theory of helical structures Shivang Agarwal, Amartya Banerjee Based on the observation that one of the most successful methods for solving the KohnSham equations for periodic systems  the planewave method  is a spectral method based on eigenfunction expansion, we formulate and implement a spectral method designed towards solving the KohnSham equations for helical structures. Various important technological materials such as nanotubes (of arbitrary chirality), nanowires, nanoribbons and miscellaneous chiral structures from chemistry and biology constitute examples of helical structures, and such systems are often associated with fascinating material properties. 
Monday, March 15, 2021 3:12PM  3:24PM Live 
C19.00002: Dissociation limit and the scaleddown selfinteraction correction Santosh Adhikari, Biswajit Santra, Kushantha Withanage, Koblar Alan Jackson, Adrienn Ruzsinszky The PerdewZunger selfinteraction correction (PZSIC), when applied to a (semi)local density functional approximation, removes spurious selfinteraction error (SIE) on an orbitalbyorbital basis, making the functional exact for all oneelectron systems. However, PZSIC is overcorrecting for manyelectron systems. There were several schemes introduced in the past to scaledown PZSIC in manyelectron regions. These socalled exterior scaling schemes were able to predict better equilibrium properties like atomization energies, first ionization energies, etc. compared to regular PZSIC. The problem of fractionalcharge dissociation of heteronuclear molecules and charged molecular ions fixed by unscaled PZSIC methods returns with these exterior scalings. A recently introduced scheme [1] based on the interior scaling of PZSIC shows promising results for equilibrium properties like first ionization energies, electron affinities, atomization energies, barrier heights of chemical reactions, etc. In this work we are investigating the behavior of this recently proposed scheme on the dissociation of heteronuclear molecules. 
Monday, March 15, 2021 3:24PM  3:36PM Live 
C19.00003: Kinetic energy density using machine learning for orbitalfree density functional calculations Mohammed Al Ghadeer, Abdulaziz AlAswad, Fahhad Alharbi Inspired by the remarkable ongoing progress of the datadriven science approach, a predictive model is prepared to develop accurate onedimensional kinetic energy density functionals (KEDF) using Machine Learning (ML). Starting from possible analytical forms of kinetic energy density [1,2] and by utilizing a variety of solvable models, an accurate Linear Regression model is statistically trained to estimate the kinetic energy as functionals of the density. The mean relative accuracy for even a small number of randomly generated potentials is found to be better than the standard KEDF by several orders of magnitudes. As more different potentials of model problems are mixed, the coefficients of the linear model significantly approach the analytic values of ThomasFermi (TF) and von Weizsäcker (vW), suggesting the reliability of the statistical training approach. This work can provide an important step toward more accurate largescale orbital free density functional theory (OFDFT) calculations. 
Monday, March 15, 2021 3:36PM  3:48PM Live 
C19.00004: Machine learning accurate exchange and correlation functionals of the electronic density Sebastian Dick, Marivi Fernandez Here, we review recent efforts to use machine learning (ML) methods for the creation of density functionals. We showcase our own framework, NeuralXC, which is based on a projection of the electron density onto localized atomic orbitals and a functional parametrized by neural networks. The functionals thus created are designed to lift the accuracy of a baseline method towards that provided by more accurate reference calculations, all while maintaining their efficiency. We show that a meaningful representation of the physical information contained in the training data is learned, making the functionals transferable across systems. Challenges on the path to a truly universal MLfunctional are outlined and possible future approaches are discussed. 
Monday, March 15, 2021 3:48PM  4:00PM Live 
C19.00005: DataDriven ExchangeCorrelation Functional Design for Transferability and Interpretability Kyle Bystrom, Boris Kozinsky Due to its computational efficiency compared to other quantum mechanical methods, Density Functional Theory (DFT) is a popular tool in computational chemistry. Recently, machine learning (ML) has been explored as a tool to develop more accurate exchangecorrelation (XC) functionals, but more work is required to design ML models which are transferable across chemical space and can be interpreted in the context of conventional functional design. To this end, we introduce two developments to design functionals that are transferable, obey exact theoretical constraints, and have separate exchange and correlation parts. First, we design a Gaussian Processbased exchangeonly functional that obeys the uniform scaling rule and approximately matches the homogeneous electron gas limit. Second, we explore the use of the exchange energy density (both exact and ML) as a parameter for the correlation functional, effectively resulting in a more flexible local hybrid without gauge ambiguity issues. The accuracy of these approaches is competitive with semiempirical functionals and recent ML models for atomization energies, ionization potentials, and barrier heights. 
Monday, March 15, 2021 4:00PM  4:12PM Live 
C19.00006: New approximations for the exchangecorrelation potential using connector theory Ayoub Aouina, Matteo Gatti, Lucia Reining In the KohnSham formulation of density functional theory (DFT) [1], the groundstate density of interacting electrons can be obtained from a fictitious system of independent particles in an effective potential. Even though DFT is in principle exact the effective potential contains an unknown quantity called the exchangecorrelation (xc) potential. In this talk we propose a new approximation to the xc potential using a general approach called "Connector Theory" (COT) [2]. This approach is a prescription of how to use data from models to calculate quantities in materials. COT is in principle exact but in practice approximations are needed to make it useful. After introducing the general scheme of this approach, we explain how to use the COT in order to build nonlocal functionals of the density for the xc potential. We show how well the connector approximation describes the nonlocal functional and we compare with previous approximations. Finally, after implementing the connector xc potential in the selfconsistent KohnSham loop, we discuss the quality of the resulting electronic densities and band structures. 
Monday, March 15, 2021 4:12PM  4:24PM Live 
C19.00007: Enhancing the accuracy of interiorscaled PerdewZunger selfinteraction correction Puskar Bhattarai, Biswajit Santra, Kamal Wagle, Yoh Yamamoto, Rajendra R Zope, Koblar Jackson, John Perdew The Perdew Zunger selfinteraction correction (PZSIC)^{1} improves the performance of density functional approximations (DFAs) for the properties that involve significant selfinteraction error (SIE), as in stretched bond situations, but overcorrects for equilibrium properties. This overcorrection is often reduced by LSIC^{2}, local scaling of the PZSIC to LSDA. Here we propose a new scaling factor to use in an LSIClike approach that satisfies an additional important constraint: the correct coefficient of Z in the asymptotic expansion of the exchangecorrelation (xc) energy for atoms of atomic number Z, which is neglected by LSIC. LSIC+ applied to LSDA works better for many properties than LSDALSIC and the PBE GGA and gives comparable results to the SCAN metaGGA. Unlike LSIC and LSIC+, SCANsdSIC^{3}, seems to describe weak bonds correctly. However, sdSIC spoils the correct asymptotic behavior of the xc potential. Interiorscaled PZSIC with improved isoorbital indicators might be developed to work more widely than the methods considered here. 
Monday, March 15, 2021 4:24PM  4:36PM Live 
C19.00008: Accelerate stochastic calculation of randomphase approximation correlation energy difference with atombased correlated sampling YuChieh Chi, Chen Huang A kernel polynomial method (KPM) is developed to calculate the random phase approximation (RPA) correlation energy. In the method, RPA correlation energy is formulated in terms of the eigenvalues of a matrix that is the product between the Coulomb potential and KohnSham (KS) linear response function. The integration over the eigenvalues is then calculated using KPM. Since it is often the energy difference between two systems that is of much interest in practice, another focus of this work is to develop a method to accelerate the convergence of such energydifference calculations. The method is termed atombased correlated sampling (ACS). The performance of ACS is examined by calculating the isomerization energy of acetone to 2propanol and the energy of watergas shift reaction. Using ACS, the convergences are accelerated by 3.6 and 4.5 times, respectively. Methods developed in this work are expected to be useful for calculating energy differences between systems that mainly differ in certain local regions, such as calculating adsorption energies of molecules on metal surfaces for surface catalysis. 
Monday, March 15, 2021 4:36PM  4:48PM Live 
C19.00009: Can the HartreeFock kinetic energy exceed the true kinetic energy? Steven Crisostomo, Mel Levy, Kieron Burke HartreeFock (HF) theory has remained an important tool for quantum chemical calculations since its earliest appearances in the late 1920s. Despite a near century of development, the sign of the difference between the true and HartreeFock kinetic energies remains unclear for most systems. Intuition suggests that the true kinetic energy should always be larger than the HF value, but we know of no proof of this. For atoms or ions, the virial theorem shows that the true kinetic energy is always larger than its HF counterpart. Beginning from a generalized virial theorem derived from density scaling considerations, we derive a general expression for the kinetic energy difference, that applies to all systems. Calculations on Hooke’s atom illustrate this relation and show that the difference of the kinetic energies always remains positive, thereby not providing a counterexample. 
Monday, March 15, 2021 4:48PM  5:00PM Live 
C19.00010: Selfconsistency in the FermiLöwdin orbital selfinteraction correction method using the KriegerLiIafrate approximation Carlos Diaz, Tunna Baruah, Rajendra R Zope The PerdewZunger (PZ) selfinteraction correction (SIC) method provides a way to remove oneelectron selfinteraction errors on an orbitalbyorbital basis. It requires use of local orbitals as use of KohnSham orbitals leads to the sizeextensivity problem. Pederson and coworkers have shown that use of FermiLöwdin orbitals (FLOs) simplifies implementation of PZSIC. In this talk we present a selfconsistent implementation of FLOPZSIC using the KriegerLiIafrate approximation (KLI) to the optimized effective potential (OEP) and compare it to Jacobilike selfconsistent implementation of Pederson et al. [1]. Since a single Hamiltonian is diagonalized in FLOSICKLI it, unlike the Jacobi method, also provides a correction to unoccupied orbitals. We compare the results obtained using the FLOSICKLI method with the FLOSICJacobi scheme for a wide array of properties. Our results show that FLOSICKLI provides comparable results to the FLOSICJacobi for a wide array of properties. Similar to the differences between HartreeFock and exact exchange OEP HOMOLUMO gaps, we find that the HOMOLUMO gaps in FLOSICKLI are smaller than FLOSICJacobi gaps. 
Monday, March 15, 2021 5:00PM  5:12PM Live 
C19.00011: Assessing Local Hybrid Density Functionals for the Prediction of Exchange Coupling Constants in Transition Metal Complexes Henry Fitzhugh, James Furness, Jianwei Sun The prediction of SpinHamiltonian exchange coupling parameters is key for successful modelling of multicenter transition metal complexes (MTMCs) such as single molecule magnets and biocatalyst analogues. Local hybrid functionals, which include a spatially varying proportion of exact exchange, have been proposed as a method for improving the performance of density functional theory (DFT) with these highly magnetic systems. Given DFT is one of the few methods efficient enough for analysis of large MTMCs, it is crucial to understand and improve upon performance and reliability for calculation of coupling parameters and magnetic contributions to energy levels. Here we examine the performance of local hybrid and metaGGA functionals, including the new r^{2}SCAN functional, for the prediction of coupling parameters in several dinuclear transition metal complexes. Natural population analysis and qualitative density comparisons rationalize the variation in functional performance and demonstrate the need for further local hybrid functional development. 
Monday, March 15, 2021 5:12PM  5:24PM Live 
C19.00012: Towards an orbitalfree kinetic energy density functional for molecular systems Omololu AkinOjo New kinetic energy density functionals (KEDFs) for orbitalfree density functional theory (OFDFT) involving manyatoms systems are proposed. These KEDFs utilize the densities and information from properties of the constituent atoms. The performance of these KEDFs are presented for densities calculated from Hartree Fock theory, KohnSham density functional theory and for those obtained by minimizing energy functionals involving these new KEDFs. 
Monday, March 15, 2021 5:24PM  5:36PM Live 
C19.00013: Building a database of twodimensional material properties using the SCAN functional Can Ataca, Daniel Wines, Gracie Chaney, Jaron A Kropp, Fatih Ersan The strongly constrained and appropriately normed (SCAN) metaGGA functional has reportedly performed exceptionally well for density functional theory (DFT) calculations involving different crystalline systems, accurately capturing lattice constants and van der Waals (vdW) interactions. The computational cost of SCAN is less than that of the hybrid functional methods as well. SCAN has been applied to several threedimensional systems, but has not been widely used for twodimensional (2D) materials such as transition metal (M) monochalcogenides (MX), M dichalcogenides (MX_{2}), and M trichalcogenides (MX_{3}). We provide a comprehensive set of data obtained by SCAN, hybrid functionals (HSE06), and PBE. Specifically, we compare lattice constants, bandgaps, and cohesive energies. We also study optical properties with the GW approximation and BetheSalpeter equation (BSE), using wavefunctions obtained from SCAN and PBE. Our goal is to benchmark these results and create a full database to determine how SCAN performs compared to other well established DFT functionals. This work is the terminal study for benchmarking different DFT functionals and will guide further theoretical studies involving 2D materials and electronic structure method development. 
Monday, March 15, 2021 5:36PM  5:48PM Live 
C19.00014: Nonadditive kinetic potential functional V^{nad }from analytic inversion: allelectron and pseudopotential calculations Mojdeh Banafsheh, Leeor Kronik, Tim Gould, Tomasz Adam Wesolowski, David A Strubbe 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 pairs of specific 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). We discuss the constraints on the choice of electron densities to ensure their admissibility. The potential is constructed for various diatomic systems of four electrons at different interatomic distances for which the atomic densities are weakly overlapped. The results are compared to common kinetic functional approximations to assess their quality in this regime. V^{nad }is also presented for some diatomic systems including more than 4 electrons. We investigate the behavior around the nuclei, where cusps appear in the density, and compare results for allelectron and pseudopotential calculations. We demonstrate the application in embedding theory by solving for a subsystem with V^{nad }as an additional potential. In addition, the well known step structure associated with molecular dissociation is studied from the analytically inverted potential. 
Monday, March 15, 2021 5:48PM  6:00PM Live 
C19.00015: Investigation of Electronic and Optical Properties of CopperCysteamine with Halogens Noura Alkhaldi, Muhammad Huda, Wei Chen, Nil Kanatha Pandey, Manbo Zhang Copper cysteamine (CuCy) is molecular solids with layers structure. It has a strong luminescence that can be used in imaging. Besides, CuCy is a photosensitizer which can be activated by visible light, Xrays, microwaves, and ultrasound to generate reactive oxygen species (ROS) to treat the cancer and infection diseases. Understanding the electronic and optical properties of CuCy is crucial. In this presentation, density functional theory (DFT) is used to study the electronic and optical properties of CuCyX, with X= F, Cl, Br, I. We have started with studying the stability of CuCy structures considering different states. Different spinmultiplicities along with spinorbitcoupling (SOC) is considered to understand the electron transition from the occupied to the unoccupied bands. Point defects are made as well in the pristine structures of CuCy to study how those affect the stability of the structures. Our computed data is in good agreement with the experimental results. 
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