Interaction of helium with a metal surface

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Abstract
A theory is given for the interaction of a helium atom with a metal surface. The basic theory is a generalisation of that used by Zaremba and Kohn (1977) for jellium surfaces, and relates the interaction to shifts of the band energies due to the presence of the helium. The authors show that these shifts can be determined via perturbation theory in the non-local helium pseudopotential. The first-order expression is particularly simple and demonstrates the physical origin of the interaction in terms of a balance between the kinetic energy cost when the Bloch tails orthogonalise to the helium 1s orbital and the potential energy gained in the field of the helium atom. For jellium, higher-order corrections are shown to contribute only approximately 15% to the interaction. The first-order result should therefore give a reasonably accurate picture of the corrugation profiles probed by low-energy helium particles.