Use of FLOSIC for understanding anion-solvent interactions

Abstract

An Achille’s heel of lower-rung density-functional approximations is that the highest-occupied-molecular-orbital energy levels of anions, known to be stable or metastable in nature, are often found to be positive in the worst case or above the lowest-unoccupied-molecular-orbital levels on neighboring complexes that are not expected to accept charge. A trianionic example, [Cr(C2O4)3]3−, is of interest for constraining models linking Cr isotope ratios in rock samples to oxygen levels in Earth’s atmosphere over geological timescales. Here we describe how crowd sourcing can be used to carry out self-consistent Fermi–Löwdin–Orbital-Self-Interaction corrected calculations (FLOSIC) on this trianion in solution. The calculations give a physically correct description of the electronic structure of the trianion and water. In contrast, uncorrected local density approximation (LDA) calculations result in approximately half of the anion charge being transferred to the water bath due to the effects of self-interaction error. Use of group-theory and the intrinsic sparsity of the theory enables calculations roughly 125 times faster than our initial implementation in the large N limit reached here. By integrating charge density densities and Coulomb potentials over regions of space and analyzing core-level shifts of the Cr and O atoms as a function of position and functional, we unambiguously show that FLOSIC, relative to LDA, reverses incorrect solute-solvent charge transfer in the trianion-water complex. In comparison to other functionals investigated herein, including Hartree–Fock and the local density approximation, the FLOSIC Cr 1s eigenvalues provide the best agreement with experimental core ionization energies.

DOCSIC: A Mean-Field Method for Orbital-by-Orbital Self-Interaction Correction

“…SIE is the origin of several well-documented failures of lower-rung density-functional approximations, such as the incorrect potential energy dissociation curve for asymmetric species 5,6 or the too high highest-occupied-molecular-orbital energy levels of negatively charged fragments, making their charge too positive. 7 In 1981, Perdew and Zunger proposed a scheme to remove the one-electron SIE 8 on an orbital-by-orbital basis. This scheme, usually known as Perdew−Zunger (PZ) selfinteraction correction (SIC) is based on a modified orbitaldependent energy functional,…”

“…Density functional theory (DFT) , is widely used as the workhorse of electronic structure calculations thanks, in part, to its compromise between accuracy and computational efficiency. , One of the most remarkable drawbacks of approximate exchange-correlation (XC) density functionals is their inability to cancel the self-interaction (SI) of electrons, which gives rise to the well-known self-interaction error (SIE) problem. SIE is the origin of several well-documented failures of lower-rung density-functional approximations, such as the incorrect potential energy dissociation curve for asymmetric species , or the too high highest-occupied-molecular-orbital energy levels of negatively charged fragments, making their charge too positive …”

“…SIE is the origin of several well-documented failures of lower-rung density-functional approximations, such as the incorrect potential energy dissociation curve for asymmetric species 5 , 6 or the too high highest-occupied-molecular-orbital energy levels of negatively charged fragments, making their charge too positive. 7 …”