A first-principles comparative study of exchange and correlation potentials for ZnO

Selection of a proper exchange and correlation potential for efficient treatment of excited-state properties such as the electronic band structure is required in density functional theory (DFT). We propose a simple and efficient Engel–Vosko generalized gradient approximation (GGA-EV) for calculating the electronic and optical properties of different phases of ZnO, namely, wurtzite, rock salt, zincblende and the CsCl-type structure. To validate our approach, we compare the results to those obtained using the local density approximation (LDA-PW91) and the parameterized generalized gradient approximation of Perdew et al. (GGA-PBE). We calculated the band structure, density of states, crystal field splitting energy, dielectric function, reflectivity, and absorption coefficient. GGA-EV yielded a wider valence band and narrower d-band in comparison to LDA-PW91 and GGA-PBE. Moreover, GGA-EV resulted in greater separation between Zn d and O p states, which reduced pd repulsion and consequently improved the energy band gap.