High-coverage adsorption of alkali metals at the CaO and MgO (100) surfaces

The interaction of alkali metals (Li and Na) with the defect-free (100) surface of CaO and MgO has been studied in the framework of density functional theory with periodic boundary conditions for the coverages 1.0 and 0.5 ML (Li) and 0.5 ML (Na). The lateral interaction among adsorbed alkali atoms contributes significantly to the stabilization of the metallic layer. The binding energy of Li for the 1.0 ML coverage is comparable for CaO and MgO and is larger than the cohesive energy of bulk Li. Hence, this monolayer is stable with respect to formation of a three-dimensional metallic island, and a small lattice mismatch between MgO(100) and the bcc Li indicates the possibility of creating a low-energy interface between these two materials under proper growth conditions. The chemical effects in the metal–substrate interaction are not significant.