Approximations to the exact exchange potential: KLI versus semilocal

TL;DR

This paper compares the KLI approximation and semilocal potentials, especially Becke-Johnson, to the exact exchange potential in density functional theory, highlighting their relative accuracy and differences in complex materials.

Contribution

It extends previous comparisons by including the KLI approximation, a beyond-semilocal method, and evaluates its performance against semilocal potentials.

Findings

KLI and BJ potentials are most reliable approximations.

Significant differences observed in transition-metal oxides.

KLI captures beyond-semilocal effects better in some cases.

Abstract

In the search for an accurate and computationally efficient approximation to the exact exchange potential of Kohn-Sham density functional theory, we recently compared various semilocal exchange potentials to the exact one [F. Tran et al., Phys. Rev. B 91, 165121 (2015)]. It was concluded that the Becke-Johnson (BJ) potential is a very good starting point, but requires the use of empirical parameters to obtain good agreement with the exact exchange potential. In the present work, we extend the comparison by considering the Krieger-Li-Iafrate (KLI) approximation, which is a beyond-semilocal approximation. It is shown that overall the KLI and BJ-based potentials are the most reliable approximations to the exact exchange potential, however, sizeable differences, especially for the antiferromagnetic transition-metal oxides, can be obtained.