Spin–orbit and modified Becke–Johnson potential effects on the electronic properties of bulk Ge: A density functional theory study

Abstract

The recently proposed modified Becke–Johnson exchange potential with LDA (local density approximation) correlation (MBJLDA) (Tran and Blaha, 2009 [19]) is employed to study the electronic structure of bulk Ge. Combining this MBJLDA potential with spin–orbit (SO) interactions and LDA pseudopotentials within the plane wave density functional method, leads to results that are generally superior to those obtained from far more sophisticated and computationally expensive methods such as GW. The semiconducting state of bulk Ge is obtained with an indirect energy gap of 0.87 eV and a valence band width of 12.79 eV, in very good agreement with the measured values of 0.74–0.84 eV and 12.6–12.9 eV, respectively. The pressure (lattice constant) dependence of the individual energy levels calculated with the MBJLDA xc potential and SO interactions also provides a good description of the experimental data, equal to that of recent quasiparticle self-consistent GW (QSGW) calculations. Combining the MBJLDA xc potential and SO interactions with GGA (generalised gradient approximation) atomic pseudopotentials led to inferior results for bulk Ge. The relevance of the obtained results for modelling nanostructured Ge is briefly discussed.