Electronic screening at the surface of an sp-bonded metal

A review is given of recent work on the screening response of the conduction electrons at a simple metal surface. Particular emphasis is placed on the density response function at wave vector transfers typical of electronic excitations involved in, e.g., coupling to an adsorbate. This means that q|| (the wave vector transfer parallel to the surface) can range from a small fraction of kF to q|| > kF, where kF is the Fermi wave vector. This necessitates an entirely microscopic description of the screening process. The solution of the self-consistent problem for the ground state is considered first (for the jellium model). The response problem is then addressed within self-consistent field response theory. The physical model used in the evaluation of the effective potential in the ground state determines the dynamical model for the response function. Several response theories are discussed in unison according to the procedure used to introduce (or entirely drop, as in the case of the random-phase approximation) the many-body effects of exchange and correlation. Applications to dynamic and static screening processes are considered. Examples of dynamical processes are the damping of a vibration of an adsorbed molecule due to decay into electron-hole pairs, and the excitation of collective modes in an atomically-thin overlayer of alkali-metal atoms adsorbed on a metal surface. In the static limit, recent work on lattice relaxation at Al(110) is discussed. In each case contact is made with the relevant experimental evidence.