The Fermi-L\"owdin self-interaction correction for ionization energies of organic molecules

TL;DR

This paper evaluates a Fermi-L"owdin self-interaction correction method for improving ionization energy calculations in organic molecules, showing significant but nuanced improvements over standard density functional approximations.

Contribution

It introduces a scaled self-interaction correction based on the iso-orbital indicator to better estimate ionization energies in organic molecules.

Findings

Self-interaction corrected DFAs improve ionization energy estimates.

Scaling the correction reduces overestimation of ionization energies.

Method significantly enhances the description of highest-occupied orbital eigenvalues.

Abstract

(Semi)-local density functional approximations (DFAs) suffer from self-interaction error (SIE). When the first ionization energy (IE) is computed as the negative of the highest-occupied orbital (HO) eigenvalue, DFAs notoriously underestimate them compared to quasi-particle calculations. The inaccuracy for the HO is attributed to SIE inherent in DFAs. We assessed the IE based on Perdew-Zunger self-interaction corrections on 14 small to moderate-sized organic molecules relevant in organic electronics and polymer donor materials. Though self-interaction corrected DFAs were found to significantly improve the IE relative to the uncorrected DFAs, they overestimate. However, when the self-interaction correction is interiorly scaled using a function of the iso-orbital indicator z{\sigma}, only the regions where SIE is significant get a correction. We discuss these approaches and show how these methods significantly improve the description of the HO eigenvalue for the organic molecules.