Cluster modeling of metal oxides: case study of MgO and the CO MgO adsorption system

Three principles, namely, a neutrality principle, a stoichiometry principle , and a coordination principle are proposed as criteria for building up clu ster models of metal oxides. Particular attention is focused on how to cut out a stoichiometric cluster which possesses the smallest boundary effect f or a given cluster size. Several criteria for determining self-consistently the magnitudes of embedding point charges are discussed. The problem of ho w the methods of embedding affect the calculated electronic properties of t he substrate cluster and the adsorption properties are investigated. It is that a better cutout cluster, which interacts less with its surroundings, w ould depend less on the embedding scheme, while a better description of the surroundings would improve the quality of the cutout cluster. A simple poi nt charge model provides a stable model of the oxide surface as well as of adsorption on the surface.