Core-hole excitations using the projector augmented-wave method and the Bethe-Salpeter equation

TL;DR

This paper develops and validates a Bethe-Salpeter equation implementation within the projector augmented-wave method to accurately model core-hole excitations, showing excellent agreement with experiments and improvements over previous methods.

Contribution

The paper introduces a novel implementation of the Bethe-Salpeter equation for core excitations using the projector augmented-wave method, enhancing accuracy over existing approaches.

Findings

Excellent agreement with experimental spectra for various materials.

Supercell core-hole method sometimes lacks fine spectral details.

BSE captures features missed by the core-hole method, especially in complex cases.

Abstract

We present an implementation of the Bethe-Salpeter equation (BSE) for core-conduction band pairs within the framework of the projector augmented-wave method. For validation, the method is applied to the $K$-edges of diamond, graphite, hexagonal boron-nitride, as well as four lithium-halides (LiF, LiCl, LiI, LiBr). We compare our results with experiment, previous theoretical BSE results, and the density functional theory-based supercell core-hole method. In all considered cases, the agreement with experiment is excellent, in particular for the position of the peaks as well as the fine structure. Comparing BSE to supercell core-hole spectra we find that the latter often qualitatively reproduces the experimental spectrum, however, it sometimes lacks important details. This is shown for the $K$-edges of diamond and nitrogen in hexagonal boron-nitride, where we are capable to resolve within the BSE experimental features that are lacking in the core-hole method. Additionally, we show that in certain systems the supercell core-hole method performs better if the excited electron is added to the background charge. We attribute this improved performance to a reduced self-interaction.