Nature of Xenon adsorption on graphite: On-top versus hollow site preference

We study the interaction between Xe adatoms and the graphite (0001) surface employing all-electron density-functional theory calculations. Xe adatoms prefer to adsorb in the hollow site, which is consistent with a recent dynamical low-energy electron diffraction intensity analysis. We explain the hollow site preference as a consequence of the greater polarization of Xe adatoms at the hollow site, as well as of the surface C atoms, and hence a greater induced dipole moment, which provides a larger contribution to the attractive interaction. As a consequence, Xe adatoms get closer to the surface in the hollow site. The above-mentioned mechanisms of the interaction between Xe atoms and graphite (0001) are, thus, very similar to the picture recently proposed for rare-gas adatoms on close-packed metal surfaces.