From Densities to Potentials: Benchmarking Local Exchange-Correlation Approximations

TL;DR

This paper benchmarks local exchange-correlation approximations by comparing Kohn-Sham potentials derived from quantum Monte Carlo densities with those from popular density functional approximations, revealing insights into their differences and limitations.

Contribution

It introduces a method to invert QMC densities to obtain benchmark Kohn-Sham potentials for insulators and semiconductors, enabling direct comparison with density functional approximations.

Findings

DFAs produce similar densities despite different potentials

QMC-KS gaps are generally larger than DFA gaps

KS gap sensitivity to semicore states affects experimental comparisons

Abstract

Using the Kohn-Sham (KS) inversion method of Hollins et al. [J. Phys.: Condens. Matter 29, 04LT01 (2017)], we invert densities from variational and diffusion quantum Monte Carlo (QMC) calculations to obtain benchmark QMC-KS potentials for a range of insulators and semiconductors, which we then compare to the KS potentials of popular density functional approximations (DFAs). Our results show that different DFAs yield similar electron densities, despite differences in their KS potentials, which originate primarily from the exchange and correlation contribution. We also find that the KS gap from the QMC density is typically larger than the KS gaps of most DFAs, with the exception of Hartree-Fock. Finally, the KS gap is sensitive to the inclusion of semicore states in the pseudopotentials, such that comparison with experiment should be done with caution.