Theoretical study of the relative stability of wurtzite and rocksalt phases in MgO and GaN

We report local density functional calculations using the full-potential linearized muffin-tin orbital method for MgO and GaN in the wurtzite and rocksalt structures and for orthorhombic structures along a homogeneous strain transition path linking wurtzite to rocksalt. MgO is found to be unstable in the wurtzite and marginally metastable in a layered hexagonal phase, labeled h-MgO, in which Mg is approximately fivefold coordinated, the stable phase being rocksalt. GaN is stable in the wurtzite at ambient pressures but exhibits a phase transition to the rocksalt. Band structures and charge densities exhibiting the bond formation as one goes from one structure to the other are presented.