Effective-medium theory of chemical binding: Application to chemisorption

An approximate theory of the total energy change connected with the embedding of an atom in an inhomogeneous host is developed. The primary effect of the inhomogeneous environment is included by replacing it with a homogeneous electron gas of a density equal to that of the host at the atom site. The lowest-order corrections to this simple picture are derived. The scheme, which is computationally very simple, is tested against first-principles calculations for several chemisorption systems. It is found that including a simple first-order correction gives excellent agreement for H and O adsorbates. For less electronegative atoms like Si and Li, it seems that a second-order term involving the polarizability of the atom in a homogeneous electron gas must be included.