Computational study of the structural phase transitions and pressure dependent electronic structure of ZnO

Abstract

We use rst-principles calculations based on density functional theory to study the structural properties and pressure-induced solid-solid phase transitions of ZnO. Both the local-density approximation (LDA) and the PBE96 form of the generalized gradi- ent approximation (GGA) are employed together with the projector augmented wave (PAW) method to mimic the electron-ion interaction. The electronic structure is investigated by the HSE hybrid functional and a partially self-consistent GWapprox- imation. We consider the wurtzite (B4), rocksalt (B1), zinc blende (B3), CsCl (B2), PbO (B10), NaTl (B32), WC (Bh), BN (Bk), NiAs (B81) and AsTi (Bi) modi cations of ZnO. The calculated structural properties in the B4, B3, B1 and B2 phases compare acceptably well with those found in previous theoretical studies, as is the transition pressure between them. We nd that the B4 phase is the most preferred low-pressure candidate in ZnO while the B2 phase is favorable at high pressures. Apart from the previously reported B4!B1!B2 phase transition, our study reveals other possible paths for a transition from B4 to B2 phase with the Bk, Bh, B10, and B81 structures as intermediate phases. It is found that the HSE and the GW approach o¤er a signif- icant improvement to the prediction of band-gaps in ZnO. The band-gaps are found to increase with increasing pressure leading to the structural phase transitions.