Adsorbate-induced changes of linear and nonlinear electronic-response properties and second-harmonic generation at simple metal surfaces.

Abstract

We present a formalism to calculate the change of linear and nonlinear response properties induced by single atoms adsorbed on simple metal surfaces in the adiabatic limit. The atom plus jellium model of Lang and Williams for adsorbate chemisorption was extended to incorporate the presence of an external static field. On the basis of these first-principles calculations in the frame of density-functional theory the mechanisms for the increase or decrease of second-harmonic generation by a number of representative adsorbate atoms on free-electron-like jellium substrates are discussed and correlated with the various orders of the adatom and substrate response. The dipole field of the adsorbed atom causes an important long-range contributon to the response. These dipole fields also give external-field screening and depolarization and lead to a quantitative model for adatom-adatom interactions in the low-coverage regime. The results of recent SHG experiments are interpreted with our approach.