Exact-exchange calculations of the electronic structure of AlN, GaN and InN Original Research Article

The electronic structure of the zincblende (ZB) phase of AlN, GaN and InN has been investigated by using the exact-exchange (EXX) Kohn–Sham density functional theory, with the Ga 3d and In 4d electrons treated both as valence states and as part of the frozen core. Our EXX bandgaps for AlN and GaN (obtained with the semicore Ga 3d electrons included as core states) are found to be in good agreement with previous EXX calculations, GW results and available experimental data. When the semicore d electrons are treated as valence states, the EXX bandgap of ZB-GaN is found to be in excellent agreement with the GW results. However, both the EXX and GW bandgaps are about 0.4 eV smaller than experiment. For InN, where the application of the GW approach is problematic, due the negative LDA bandgap, the EXX approach allows for a fully consistent treatment. Contrary to common belief, the removal of the self-interaction, by the EXX approach, does not account for the large discrepancies between the LDA (or GGA) results and experiment for the position of the semicore d bands.