Stability of rocksalt polar surfaces: An ab initio study of MgO(111) and NiO(111)

The structures of the (100) and the polar (111) surfaces of the rocksalt materials MgO and NiO have been studied using ab initio all electron total energy calculations, employing local basis sets, and a hybrid density functional (B3LYP). Various schemes for the stabilization of the polar surface have been examined, and we find that the hydroxylated (111) surfaces are more stable than the clean (100) surfaces. The computed energies suggest that the clean (111) surface of MgO is unstable with respect to faceting into (100) microfacets, while for the NiO(111) surface the octopolar reconstruction is favored. This distinction is due to the relatively high surface energy of the (100) surface of NiO.