Effect of atomic size on the effective polarizability of physisorbed atoms

Abstract Calculations of the effective polarizability of atoms adsorbed on metal surfaces have usually represented the atom by a polarizable point dipole. A simple model which includes an atomic size parameter but neglects exchange and correlation effects between the atom and the metal is used to investigate the validity of the polarizable point atom approach. A gradient expansion technique within the density functional formalism is used in this calculation. Results indicate that atomic size can greatly reduce the enhancement of the effective polarizability found from the polarizable point atom approximation.