Theory of helium adsorption on simple and noble-metal surfaces

The repulsive part of the helium-metal physisorption potential is calculated in the Hartree-Fock approximation. To the lowest order in the overlap ($S$) between the atomic and metallic wave functions, this interaction is determined by the change in the single-particle density of states of the metal. Combined with a previous calculation of the Van der Waals interaction, helium-metal potentials are derived for the simple and noble metals using a jellium model for the metal. Binding energies and equilibrium positions of the helium atom are determined. For the simple metals, the binding energy decreases with increasing $r_s$. Its value for the noble metals is between 40 and 70 K. The equilibrium positions are found to be between 3 and 7 Å (relative to the jellium background) for all the metals studied.