Density functionals with spin-density accuracy for open shells

TL;DR

This paper discusses how correcting the approximation in density functional theory (DFT) for open shell systems can make DFT as accurate as spin-DFT, especially in the limit of zero magnetic field.

Contribution

It introduces a correction to DFT that improves its accuracy for open shell systems, aligning it with spin-DFT in zero magnetic field conditions.

Findings

Corrected DFT can match SDFT accuracy for open shells.

Kohn-Sham equations of SDFT emerge as generalized KS equations of DFT.

Enhances the applicability of DFT to open shell systems.

Abstract

Electrons in zero external magnetic field can be studied with density functional theory (DFT) or with spin-DFT (SDFT). The latter is normally used for open shell systems because its approximations appear to model better the exchange and correlation (xc) functional, but also because so far the application of DFT implied a closed-shell-like approximation. Correcting this error for open shells allows the approximate DFT xc functionals to become as accurate as those in SDFT. In the limit of zero magnetic field, the Kohn-Sham equations of SDFT emerge as the generalised KS equations of DFT.