SIZE AND SHAPE DEPENDENCE OF THE ELECTROSTATIC POTENTIAL IN CLUSTER-MODELS OF THE MGO(100) SURFACE

We investigated the dependence of the electrostatic potential on the s ize and the shape of various cluster models of the MgO(100) surface. B oth Mg2+ and O2- adsorption sites have been considered. The clusters w ere embedded in a large array of point charges to provide a representa tion of the Madelung potential. We found that the electrostatic potent ial in the adsorption region shows a marked dependence on the size of the cluster, in particular, for non-stoichiometric clusters where the number of cations and anions differs considerably. These oscillations are due to (a) the different contribution to the electrostatic potenti al given by a point charge or by an extended ion, and (b) by the polar ization of the ions at the cluster border. The effect of the oscillati ons in the electrostatic potential on the chemisorption properties was investigated for the case of CO2 interacting with surface and defect O2- sites of the MgO surface. (C) 1996 John Wiley & Sons, Inc.