Interaction Potential between a Helium Atom and Metal Surfaces

By employing an $S$-matrix theory for evanescent waves, we have calculated the repulsive potential between a helium atom and corrugated metal surfaces. $P$-wave interactions and intra-atomic correlation effects were found to be very important. The corrugation part of the interaction potential is much weaker than predicted by the effective-medium theory. Application to Cu, Ni, and Ag (110) surfaces gives good agreement with experiment without any adjustable parameters.