Variation of Adatom Valence-Level Positions With the Distance to a Metal Surface

Abstract

We have derived general formulas for the induced density of states (DOS) for an adsorbate on a metal and have, in particular, specialized to the limiting cases for which the adsorbate potential is weak and strong. We have shown that the energy dependence of the unperturbed local metal DOS influences strongly the induced DOS. This leads to a correlation between the effective potential of the clean metal and the adsorbate resonance position. Such a correlation has earlier been observed in first-principles calculations for adsorbates on simple metal surfaces and certain impurity levels. To illustrate these aspects, we have performed calculations for interstitial and substitutional impurities and for sodium adsorbed on aluminium.