Adsorption of isolated Cu, Ni and Pd atoms on various sites of MgO(001): Density functional studies

Results of gradient-corrected density functional calculations are presented for the adsorption of single Cu, Ni and Pd atoms on a regular MgO(001) surface. The surface has been represented by stoichiometric clusters embedded in large arrays of point charges to simulate the Madelung potential. Three adsorption sites have been compared: on-top adsorption on the oxide anion and on the magnesium cation as well as bridge adsorption over two adjacent oxide anions. The weakly adsorbed Cu atom is slightly more stabilized atop magnesium cations than in the alternative positions; however, the energy differences are small and an easy diffusion of Cu on the surface is predicted. For the significantly stronger adsorbed Ni and Pd atoms the calculations yield a clear preference to occupy the place atop oxygen anions. This finding does not support previous experimental assignments that atoms of small palladium clusters deposited on MgO(001) occupy positions on top of Mg cations.