Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session N17: Density Functional Theory in Chemical Physics VFocus
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Sponsoring Units: DCP Chair: Roland Wilcken, University of Colorado, Boulder Room: Room 209 |
Wednesday, March 8, 2023 11:30AM - 12:06PM |
N17.00001: Overcoming delocalization and static correlation errors and describing photoemission and optical excitation with ground state DFT calculations Invited Speaker: Weitao Yang We will report our development of the localized orbital scaling correction (LOSC) in overcoming systematic delocalization and static correlation errors and development of DFT for describing photoemission and optical excitation with ground state DFT calculations. LOSC is capable of correcting system energy, energy derivative and electron density in a size-consistent manner for all commonly used density functional approximations (DFAs). The LOSC and fractional spin LOSC lead to systematically improved results, including the dissociation of ionic species, single bonds, multiple bonds without breaking the space or spin symmetry, the band gaps of molecules and polymer chains, the energy and density changes upon electron addition and removal, and photoemission spectra, and energy-level alignments for interfaces. The LOSC DFA orbital energies are excellent approximations to quasiparticle energies, comparable to or better than GW. This also leads to the QE-DFT (quasiparticle energies from DFT) approach: the calculations of excitation energies of the N-electron systems from the ground state DFA calculations of the (N - 1)-electron systems. Results show good performance with accuracy similar to TDDFT for valence excitations with commonly used DFAs with or without LOSC. For charge transfer and Rydberg states, good accuracy was obtained only with the use of LOSC DFA. The QE-DFT method has been further developed to describe excited-state potential energy surfaces (PESs), conical intersections, and the analytical gradients of excited-state PESs. We have also made the LOSC software available for the community. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N17.00002: Curvature and unit-cell periodicity in the localized orbital scaling correction for bulk systems Jacob Z Williams, Weitao Yang The localized orbital scaling correction (LOSC) has shown great promise in correcting the systematic delocalization error common to density functional approximations. Recent work [1] demonstrated that Coulomb screening is necessary to apply LOSC to materials; ideally, this screening should be parameter-free and specific to each substance. Applying the exact second-order curvature operator of Mei et al. [2] addresses both concerns. We report here the development of an ab initio linear-response LOSC method for periodic boundary conditions. Utilizing the unit-cell periodic decomposition of Wannier orbital densities reported by Colonna et al. [3] improves computational efficiency. Preliminary data suggest major improvements in the computed fundamental gaps of semiconductors and insulators. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N17.00003: Quantum Learning from Element 118 Alexander I Johnson, Kusal Khandal, Kushantha Withanage, Mark R Pederson There is a rising interest in molecular magnets containing rare earth elements, due to their unique magnetic properties and the potential for ground-breaking changes in quantum computing and quantum information science. Density functional theory (DFT) is the leading theoretical tool for studying molecular magnets; however, problems arise when rare earths are included. Most likely due to self-interaction error, standard density functional theory has difficulties with highly local f-states that give rare earths their unique magnetic properties. FLOSIC is expected to improve predictions for rare earth elements yet defining initial starting points for Fermi-orbital descriptors (FODs) for heavy atoms has been a challenge with few success stories. We present a general method for generating starting FODs using C3V symmetry for all noble gases, including Og (Z=118). We show that the FODs and FLOs for Og contains all quantum information needed for starting FLOSIC calculations for all atoms regardless of their charge and spin states or ligation - including rare earth elements. Variable Z-dependent scaling, possibly using virial-like arguments, can be used to adapt the radial extent of starting FLOs and FODs. We present an existence proof which guarantees that FODs exist for any system. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N17.00004: Density corrected SCAN functional in water clusters Pradeep Bhetwal, Saswata Dasgupta, Chandra Shahi, John P Perdew, Francesco Paesani The main hurdle of Kohn-Sham Density Functional Theory (DFT)[1,2] is finding the exact exchange-correlation contribution to energy.?The accuracy of practical DFT depends not only on the choice of density functional approximations but also on the electron density produced by approximations. SCAN[3] (Strongly Constrained and Appropriately Normed) is the first meta-GGA (meta generalized gradient approximation) constrained to obey all 17 known exact constraints that a meta-GGA can. SCAN has been found to outperform most other functionals when applied to aqueous systems[4]. However, density driven errors (energy errors occurring from applying a DFA to its inexact self-consistent density) hinder SCAN from achieving chemical accuracy in some systems, including water. Density-corrected DFT (HF-DFT) alleviates this shortcoming using a more accurate electron density.?We calculated binding energies of different water clusters using Density-corrected SCAN (DC-SCAN) and find them remarkably close to reference values calculated at the CCSD(T) level of theory[5,6,7]. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N17.00005: Study of Self-Interaction Errors in Density Functional Calculations of Magnetic Exchange Coupling Constants Prakash Mishra, Yoh Yamamoto, Po-Hao Chang, Duyen B Nguyen, Juan E Peralta, Tunna Baruah, Rajendra R Zope It is well documented that self-interaction error (SIE) in density functional approximations (DFAs) is responsible for delocalization error resulting in a systematic error in the calculation of magnetic exchange coupling (J) constants. We investigate the role of SIE in DFAs belonging to the lowest three rungs of Jacob’s ladder of functionals, (namely, the local spin density approximation, Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA)and the recent SCAN family of meta-GGA functionals) on the evaluation of J coupling constants. To this end, we use three self-interaction correction (SIC) approaches that include the the Perdew-Zunger (PZSIC)1 approach,orbital (OSIC)2 and local scaling methods (LSIC)3.The molecular systems studied here are a benchmark set of H-He-H models, organic radicals, and hexa-chlorocuprates. Our results show that for the systems that mainly consist of single-electron regions, PZSIC performs well but for more complex organic systems and the chlorocuprates, an over-correcting tendency of PZSIC becomes more pronounced, and in such cases LSIC performs better than PZSIC. We find that both the density and energy corrections are crucial in order to improve the magnetic exchange coupling prediction. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N17.00006: Energetics of Transition Metal Molecules Rohan Maniar, John P. P Perdew
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Wednesday, March 8, 2023 1:06PM - 1:18PM |
N17.00007: Self-consistent implementation of locally scaled self-interaction-correction method Yoh Yamamoto, Tunna Baruah, Po-Hao Chang, Selim S Romero, Rajendra R Zope Recently proposed local self-interaction correction (LSIC) method [Zope, R. R. et al., J. Chem. Phys. 151, 214108 (2019)] is a one-electron self-interaction-correction (SIC) method that uses an iso-orbital indicator to apply the SIC at each point in space by scaling the exchange-correlation and Coulomb energy densities. The LSIC method is exact for the one-electron densities, also recovers the uniform electron gas limit of the uncorrected density functional approximation, and reduces to the well-known Perdew-Zunger SIC (PZSIC) method as a special case. We present a self-consistent implementation of LSIC within the FLOSIC scheme. The atomic forces as well as the forces on the Fermi-Lowdin orbital descriptors are also implemented for the LSIC energy functional. Results show that LSIC with the simplest local spin density functional predicts atomization energies of AE6 dataset better than some of the most widely used GGA functional (e.g. PBE) and barrier heights of BH6 database better than some of the most widely used hybrid functionals (e.g. PBE0 and B3LYP). This work shows that accurate results can be obtained from the simplest density functional by removing the self-interaction errors using an appropriately designed SIC method. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N17.00008: Revisiting the density-corrected SCAN calculations for neutral and aqueous systems Chandra Shahi, Aaron D Kaplan, John P. P Perdew The evaluation of the energy functionals on the Hartree-Fock density is a way to mitigate the delocalization error of the semi-local density functionals- often called density correction. Recent works [1,2] have reported that the density-corrected SCAN meta-GGA (DC-SCAN) achieves the accuracy of the coupled cluster theory for water. However, in a more recent work[3], we have found that the density-corrected semi-local functionals improve the barrier heights of chemical reactions because of the cancellation of the functional- and density-driven error for energy. Motivated by this, we reassessed the DC-SCAN calculations for neutral and ionic water clusters. We find that the remarkable accuracy of DC-SCAN probably comes from the error cancellation, suggesting density-overcorrection rather than a correction from the Hartree- Fock density. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N17.00009: Spin-state energy differences of octahedral Fe(II) complexes using self-interaction-corrected methods. Selim S Romero, Tunna Baruah, Rajendra R Zope Accurate prediction of spin-state energy difference is crucial for understanding the spin crossover (SCO) phenomena and is very challenging for the density functional approximations, especially for the local and semi-local approximations, due to delocalization errors. We use recent locally scaled self-interaction-correction (LSIC) [Zope, R. R. et al., J. Chem. Phys. 151, 214108 (2019)] and Perdew-Zunger self-interaction-correction (PZSIC) method to study the spin-state gaps (SSG) of Fe(II) complexes with four different ligands of various strengths and compare them with reference diffusion Monte Carlo (DMC) results. Results show the surprising failure of the PZSIC method, which favors low spin states for all systems. The perturbative LSIC-LSDA using PZSIC densities significantly improves the gaps with a mean absolute error of 0.51 eV but slightly overcorrects PZSIC for the stronger ligand. The quasi self-consistent LSIC method with the simplest LSDA functional gives the correct sign of SSG for all ligands with a mean absolute error (MAE) of 0.56 eV, comparable to that of CCSD(T) (MAE = 0.49 eV). |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N17.00010: Nonlinear effects in Many-body van der Waals Interactions Lilia M Woods Van der Waals dispersive interactions play an essential role in the stability of materials composed of layered chemically inert components. A systematic understanding of properties determining such longe ranged interactions is of great importance for heterostructures, biological or colloidal materials, as well as nanostructured devices. Many recently discovered materials, such as transition metal dichalcogenides, exhibit strong optical nonlinearity. While van der Waals interactions are studied within linear response properties, nonlinear effects are practically unexplored. In this study, we propose a generalized coupled dipole method that includes the atomic structure and the atomic linear and nonlinear polarizabilities on an equal footing. Through a modified Hamiltonian approach, the van der Waals interaction can be calculated by taking into account all many-body effects and system anisotropy. Using perturbation theory, we are able to give a qualitative comparison between factors responsible for linear and nonlinear contributions in the interaction. This investigation broadens the basic physics of dispersive interactions especially in the context of nonlinear materials. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N17.00011: Density Matrix Renormilization Group and Pair-Density Functional Theory for Molecular Excited States Daniel King, Zihan Pengmei, Laura Gagliardi Density matrix renormalization group theory has proven a highly flexible and efficient ansatz for converging molecular wave functions. However, large-scale studies of its convergence properties with respect to bond dimension and orbital character are rare. In this work, we investigate the performance of DMRG on a broad and diverse dataset of vertical excitation energies, and propose diagnostics for identifying when the DMRG ansatz has converged to an inaccurate local minima or when more orbitals need to be included in the active subspace. Additionally, we examine the convergence behavior of the DMRG excitation energy when non-classical correlation is approximated utilizing pair-density functional theory (DMRG-PDFT). Our findings show that DMRG-PDFT is able to converge to a quantitatively accurate result much more rapidly than DMRG alone, making DMRG-PDFT a promising approach for the study of strongly correlated molecular systems. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N17.00012: Understanding density driven errors via reaction barrier heights Raj K Sah, Aaron D Kaplan, Chandra Shahi, Pradeep Bhetwal, John P. P Perdew Density functional approximations can be computationally effective and otherwise correct, but they are plagued with delocalization errors. It is often suggested that a semi-local DFA be evaluated non-self-consistently on the Hartree-Fock (HF) density as a computationally simple fix for delocalization problems. This method can reach remarkable accuracy for complex meta-GGAs like SCAN. This HF-DFT is often presumed to work because the HF density is more accurate than the self-consistent DFA density. We demonstrate that the HF-DFT works for barrier heights by making a localizing charge transfer error or density over-correction, which results in a somewhat reliable cancellation of density- and functional-driven errors. This pattern is supported by a quantitative investigation of the charge transfer error in a reaction transition state. For the huge BH76 database of barrier heights, we lack the exact functional and exact electron densities that would be required to assess the precise density- and functional-driven inaccuracies. Instead, we have found and used three totally non-local functionals (the SCAN 50% global hybrid, the range-separated hybrid LC-PBE, and SCAN-FLOSIC) and their self-consistent densities as proxies. These functionals were chosen because they produce self-consistent barrier heights that are quite precise and because their self-consistent total energies are nearly piecewise linear in fractional electron number - two important similarities to the exact functional. |
Wednesday, March 8, 2023 2:18PM - 2:30PM |
N17.00013: Self-interaction correction for Solvated Anions Kushantha Withanage, Yoh Yamamoto, Priyanka Bholanath B Shukla, Alexander I Johnson, Zahra Hooshmand Gharehbagh, Karl Johnson, Rajendra R Zope, Tunna Baruah, Juan E Peralta, Koblar A Jackson, Der-you Kao, Mark R Pederson Due to unphysical self-interaction error (SIE), density functional approximations (DFAs) predict electronic orbital energies well above experiment, even in neutral systems. The problem becomes especially severe in anionic systems, where positive DFA orbital energies imply unbound electrons. Through the use of the Perdew-Zunger self-interaction correction (PZSIC), within the novel Fermi-Löwdin-orbitals (FLOSIC method) implementation, physically meaningful orbital energies can be obtained for anionic systems. We show this by applying the FLOSIC method to the extreme case of a trianionic Cr complex embedded in a water cluster. A challenge within FLOSIC is the automated determination of an initial starting point for systems as it is a prerequisite to achieving self consistency. Therefore, in this talk, we share a simple but efficient way to meet this challenge. We discuss the degree to which these simplified starting points should be viewed as density-based or density-matrix based starting points. Our results show that the HOMO of the trianion lies below the LUMO states of the water molecules even for the case where the water ball is so large that the water LUMO states reproduce the experimental electron affinity of a water cluster. |
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