Combining GW calculations with exact-exchange density-functional theory: An analysis of valence-band photoemission for compound semiconductors

TL;DR

This paper combines GW calculations with exact-exchange DFT to improve the accuracy of valence-band photoemission predictions for certain semiconductors, emphasizing the importance of the OEPx approach for better core-valence exchange treatment.

Contribution

It introduces a combined GW and OEPx DFT approach for more accurate electronic structure calculations of semiconductors, highlighting the significance of using OEPx pseudopotentials.

Findings

OEPx improves d-electron hybridisation description.

OEPx-based quasiparticle bands align better with photoemission data.

Combining GW with OEPx offers a more reliable method than LDA-based approaches.

Abstract

We report quasiparticle-energy calculations of the electronic bandstructure as measured by valence-band photoemission for selected II-VI compounds and group-III-nitrides. By applying GW as perturbation to the ground state of the fictitious, non-interacting Kohn-Sham electrons of density-functional theory (DFT) we systematically study the electronic structure of zinc-blende GaN, ZnO, ZnS and CdS. Special emphasis is put on analysing the role played by the cation semicore d-electrons that are explicitly included as valence electrons in our pseudopotential approach. Unlike in the majority of previous GW studies, which are almost exlusively based on ground state calculations in the local-density approximation (LDA), we combine GW with exact-exchange DFT calculations in the optimised-effective potential approach (OEPx). This is a much more elaborate and computationally expensive approach. However, we show that applying the OEPx approach leads to an improved description of the d-electron hybridisation compared to the LDA. Moreover we find that it is essential to use OEPx pseudopotentials in order to treat core-valence exchange consistently. Our OEPx based quasiparticle valence bandstructures are in good agreement with available photoemission data in contrast to the ones based on the LDA. We therefore conclude that for these materials OEPx constitutes the better starting point for subsequent GW calculations.