Anharmonicity in rare-gas monolayers

We have calculated the energy and atomic positions of possible ground-state configurations of Kr and Xe monolayers physiadsorbed on graphite for different coverages. We do this by expanding in a Fourier series the modulation of the atomic positions. In so doing, we extend the previous work of Shiba by (1) using microscopic pair potentials, (2) taking into account the discreteness of the lattice, and (3) including anharmonic terms. It is found that the cubic term in the expansion of the rare-gas pair potential is significant for Kr, but not for Xe. Excellent agreement is found with previous calculations using a different approach.