Hybridization between the helium $1s$ orbital and the unoccupied metal states is corrugated in the opposite sense to the charge density. This explains the anomalous smoothness observed in helium diffraction for metal surfaces. With a simple model which includes hybridization for Ni, Cu, Pd, and Ag(110) surfaces, we obtain corrugations, softness, and well depths which are in good agreement with experiment, and also agree with self-consistent calculations of charge density.

• Received 23 March 1984

DOI:https://doi.org/10.1103/PhysRevLett.53.838