First-principles study of the orthorhombic mechanism for the B3/B1 high-pressure phase transition of ZnS

Ab initio periodic DFT-LCAO methods (B3LYP and LDA functionals), at the all-electron level, were employed to study the atomic pathway of the zinc blende to rocksalt phase transition of ZnS. By the technique of constant pressure enthalpy minimization, the transformation mechanism based on a Pmm2 orthorhombic intermediate structure, recently proposed for SiC, was examined and compared to the traditional R3m rhombohedral pathway. At the equilibrium pressure of 19 GPa, an activation enthalpy of 0.15 (Pmm2) against 0.50 (R3m) eV was obtained, confirming the orthorhombic mechanism to be definitely most favored also for a more ionic solid such as ZnS. The band gap is predicted to narrow progressively from zinc blende to rocksalt, with a parallel increase of the Zn to S charge transfer. Some structural and electronic features indicate a jumplike character of the transformation mechanism at about one third of the path