  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.

Materials Science