Density functional study of M-4 clusters (M = Cu, Ag, Ni, Pd) deposited onthe regular MgO(001) surface

The interaction of square-planar M-4 clusters (M = Ag, Cu, Ni, Pd) with the ideal Mgo(001) surface has been investigated using a gradient-corrected de nsity functional (DF) method and substrate model clusters for adsorption si tes in the vicinity of O2- centers. Polarization of the adsorbed metal clus ters due to the surface electric field provides an important contribution t o metal-oxide bonds. No significant elongation of the M-M bond relative to free square-planar Mg species is calculated in adsorbed clusters, with Pd, exhibiting the largest expansion of 0.1 Angstrom. At variance with Ni and C u, for Pd and Ag only a moderate energy expense is required to sufficiently lengthen the M-M bonds such that the atoms are put in their most favorable adsorption positions on MgO close to surface O(2- )anions. (C) 1999 Elsevi er Science B.V. All rights reserved.