Satellite valleys and strained band gap transition of bulk Ge: Impact of pseudopotential approximations on quasiparticle levels

A first principles study of the electronic structure of strained Ge is carried out within the framework of plane wave pseudopotential density functional theory (DFT) combined with the GW approximation to the self-energy. Systematic investigations of the variations of high symmetry quasiparticle gaps over for a range of pseudopotential approximations are carried out. It is found that the quasiparticle corrections can be at least as sensitive to the choice of DFT approximation as to pseudopotential generation scheme, level of core-valence interaction, and pseudopotential electronic configuration. The latter can be decisive in the resulting prediction of the band gap transition strain, as the magnitudes of exchange and correlation terms involved in the quasiparticle corrections at the conduction valleys are largely determined by the arrangement of orbitals at those regions of the bandstructure, which in turn is determined by the pseudized electronic configuration.