Reversed trend in polarity for alkaline earth oxides - an ab initio study

First principles calculations show the expected trend of increasing polarit y for the alkaline earth oxides MgO, CaO and SrO to be reversed, with MgO b eing the most ionic substance and SrO the most covalent one. The larger rad ii for Ca and Sr cations enable an effective hybridization between the p or bitals of O and the metal d electrons of Ca and Sr. In Ca and Sr metal, the 36 and 4d levels are positioned just around the Fermi level, while in the oxides they dominate the cation Valence charge. The larger lattice of SrO e nables a slightly better pd hybridization, which makes SrO somewhat less io nic than CaO.