Importance of self-interaction-error removal in density functional calculations on water cluster anions

Abstract

Accurate description of the excess charge in water cluster anions is challenging for standard semi-local and (global) hybrid density functional approximations (DFAs). Using the recent unitary invariant implementation of the Perdew-Zunger self-interaction correction (SIC) method using Fermi-Löwdin orbitals, we assess the effect of selfinteraction error on the vertical detachment energies of water clusters anions with the local spin density approximation (LSDA), Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation, and the strongly constrained and appropriately normed (SCAN) meta-GGA functionals. Our results show that for the relative energies of isomers with respect to reference CCSD(T) values, the uncorrected SCAN functional has the smallest deviation of 21 meV, better than that for the MP2 method. The performance of SIC-SCAN is comparable to that of MP2 and is better than SIC-LSDA and SIC-PBE, but it reverses the ordering of the two lowest isomers for water hexamer anions. Removing self interaction error (SIE) corrects the tendency of LSDA, PBE, and SCAN to over-bind the extra electron. The vertical detachment energies (VDEs) of water cluster anions, obtained from the total energy differences of corresponding anion and neutral clusters, are significantly improved by removing self-interaction and are better than the hybrid B3LYP functional, but fall short of MP2 accuracy. Removing SIE results in substantial improvement in the position of the eigenvalue of the extra electron. The negative of the highest occupied eigenvalue after SIC provides an excellent approximation to the VDE, especially for SIC-PBE where the mean absolute error with respect to CCSD(T) is only 17 meV, the best among all approximations compared in this work.

Implementation of Perdew–Zunger self-interaction correction in real space using Fermi–Löwdin orbitals

“…The FLOSIC method has been implemented in Gaussian-orbital-based packages and has been successfully applied to study a wide array of electronic properties. 15,16,44,[57][58][59][60][62][63][64][65][66][67][76][77][78][79] In this work, we present a formulation and implementation of the FLOSIC method in real space. The real-space formulation enables rigorous, systematic convergence for all atomic species and configurations as well as large-scale parallelism to reach larger length and time scales than previously accessible at this level of theory.…”

“…In addition, pseudopotential overlap, fixed Gaussian exponents, and/or basis contraction may contribute to differences at the shortest bond distances. 58…”

Self-interaction corrected Kohn-Sham effective potentials using the density-consistent effective potential method

“…The HOMO eigenvalues of the FLOSIC scheme have previously shown good agreement with vertical ionization potentials from CCSD(T) and experiments. 36,[56][57][58][59][60] As detailed in Sec. II, the eigenvalues in DCEP-SIC calculations are shifted such that the DCEP HOMO matches with the FLOSIC HOMO values.…”

Testing Self‐Interaction Correction for Molecules in Solution

“…One of the applied SIC approaches was the Fermi-Löwdin orbital self-interaction correction (FLO-SIC [13][14][15][16] ). Whereas previous FLO-SIC investigations focused on neutral and charged water clusters, [17][18][19][20] this study, in its application of COSMO, is also an attempt to combine FLO-SIC with continuum solvation.…”