Quasiparticle bandstructure of zincblende and rocksalt ZnO

The GW approximation [1] to many body perturbation theory represents the state of the art technique to calculate the quasiparticle correction to the band gap of solids and has been sucessfully applied to many materials. Although the GW approximation works well with pseudopotentials (PP’s) and plane wave basis sets used within Density Functional Theory Local density approximation (DFT-LDA), the II-VI materials are particularly challenging due to the strong p-d hybridization between the cation ’d’ and anion ’p’ states [2, 3]. The DFT-LDA resuslts in p-d overhybridization in the bandstructure which leads to underestimation of the calculated GW band gap. Recently, the self-consistent GW scheme [4] and quasiparticle correction based on the generalized Kohn-Sham schemes [5, 6] have been used to improve the GW band gap for II-VI semiconductors and insulators. Although these schemes make closer estimate of the band gap with the GW approximation, there is still need of an elaborate theory and it is a topic of current research. We present the GW bandgap calculated with the ABINIT [7] code, using the PP and plane wave basis set, for II-VI transparent oxides namely ZnO. The quasiparticle corrections are calculated systematically with different number of valence electrons in the cation-pseudopotential. We find that the 20-electron cation pseudopotential yields the best quasiparticle correction. The dependence of self-energy on the exchange interaction between the atomic orbitals is discussed. The postioning of the cation ’d’ energy level in the quasiparticle bandstructure is addressed. The correlation between the p-d hybridization and the underestimation of the non-self-consistent GW band gap is made through a comparison of zincblende (ZB) and rocksalt (RS) ZnO. The RS phase includes the inversion symmetry at the Gamma point in the Brillouin zone. The p and d states do not mix at the Gamma point and remain unhy-