Theory of Physisorption: He on Metals

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Abstract
The attractive and repulsive contributions to the physisorption interaction energy are derived from the assumption of weak coupling between an atom and a metal surface. Results for the physical adsorption of He atoms indicate that an accurate determination of the dynamic polarizability is essential in calculations of the attractive interaction energy using a local-dielectric-function formalism. The major contribution to the physisorption interaction is the van der Waals energy, so that the physisorption energy curve is largely temperature independent. The repulsive energy is evaluated via the density-functional method. The equilibrium distances of the atom are a monotonically increasing function of the metallic-electron density. For high electron densities the binding energy increases monotonically. Values for the adsorption energies of He on various metals are in good agreement with available experimental results.