Cluster adsorption of argon on alumina

The self-consistent unrestricted Hartree-Fock method was used to study the adsorption of argon on cluster models of ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ surfaces. We have considered surfaces parallel and perpendicular to the hexagonal $c$ axis and obtained a maximum binding of 0.5 eV, in good agreement with experiment. We propose a simple electrostatic model to account for this binding.