Avoiding Unbound Anions in Density Functional Calculations

TL;DR

This paper discusses the challenge of unbound anions in density functional theory (DFT) calculations caused by self-interaction errors, and evaluates a scheme using Hartree-Fock densities to improve DFT results.

Contribution

The study demonstrates that calculating DFT energies on Hartree-Fock densities significantly improves binding predictions for anions, surpassing traditional basis set restrictions.

Findings

DFT often fails to bind anions due to self-interaction error.

Using HF densities for DFT calculations yields better anion binding energies.

The approach is less effective for cases with spin contamination, like CN.

Abstract

Converged approximate density functional calculations usually do not bind anions, due to large self-interaction error. But Hartree-Fock calculations have no such prob- lem, producing negative HOMO energies. A recently proposed scheme for calculating DFT energies on HF densities is shown to work very well for molecules, better than the common practice of restricting the basis set, except for cases like CN, where the HF density is too inaccurate due to spin contamination.