Role of semicore states in the electronic structure of group-III nitrides: An exact exchange study

TL;DR

This study uses exact-exchange density functional theory to analyze how semicore states influence the electronic bandstructure of group-III nitrides, revealing significant effects on bandgap calculations and challenging previous assumptions about self-interaction corrections.

Contribution

It provides a detailed analysis of semicore d electrons' role in the electronic structure of AlN, GaN, and InN using an exact-exchange approach, highlighting the impact of treating semicore states as valence or core.

Findings

EXX bandgaps for AlN and GaN match previous results and experiments.

Including semicore d electrons as valence reduces bandgaps of GaN and InN.

Self-interaction correction does not explain discrepancies in semicore d electron positions.

Abstract

The bandstructure of the zinc-blende phase of AlN, GaN, InN is calculated employing the exact-exchange (EXX) Kohn-Sham density-functional theory and a pseudopotential plane-wave approach. The cation semicore d electrons are treated both as valence and as core states. The EXX bandgaps of AlN and GaN (obtained with the Ga 3d electrons included as core states) are in excellent agreement with previous EXX results, GW calculations and experiment. Inclusion of the semicore d electrons as valence states leads to a large reduction in the EXX bandgaps of GaN and InN. Contrary to common belief, the removal of the self-interaction, by the EXX approach, does not account for the large disagreement for the position of the semicore d electrons between the LDA results and experiment.