A comparative study of Ag and Cu adhesion on an MgO(001) surface

Ab initio calculations were performed on 2D slab models of copper and silver adhesion on a perfect MgO(001) surface using density functional theory (DFT) combined with the localized atomic wave functions, as implemented in both CRYSTAL-98 and CRYSTAL-03 computer codes. To clarify the nature of the interfacial bonding, we consider slab models of the Ag/MgO(001) and Cu/MgO(001) interfaces with six different substrate coverages, varied from 1/4 monolayer (ML) up to 2 ML. The dependence of several key interface properties on the substrate coverage is analyzed. For all coverages, the most favorable sites for the adsorption of metal atoms are found to be above the surface O^2- ions, whereas Cu atoms are found to be more strongly bonded on a magnesia substrate, with shorter bond lengths ^zCu-O^2- . Our calculations indicate that a weak atomic polarization induces the interaction between the metal atoms and the defect-free MgO substrate and gives the dominant contribution to the bonding on the regular interfaces. Growth of metal coverage simultaneously reduces the binding energy with substrate per adatom and enhances the interatomic interaction inside the metal adlayer.