Ground-state properties of xenon on graphite

Abstract

We have calculated the classical energy associated with different possible configurations of xenon overlayers physisorbed on the graphite basal plane. A comparison is made with a previous calculation of krypton on graphite. The sensitivity of the results to the parametrization of the Xe-graphite interaction is investigated. For the weakly modulated atom surface potential suggested by Steele, the lowest energy per atom is found to occur for a hexagonal incommensurate structure with a surface coverage less than that of the $\sqrt{3}\times \sqrt{3}$ configuration. A larger modulation leads to higher coverages until eventually the ground state becomes registered. The best agreement with experimental observations occurs for a surface adatom potential whose modulation is slightly weaker than the interaction recently suggested by Klein et al. In all cases considered, the hexagonal configuration is favored and the "domain walls" are very broad (∼100 Å). We have also calculated, both for Xe and Kr, the coverage beyond which it becomes energetically advantageous to form a double layer.