Thermal excitation in a spatially modulated monolayer solid: Incommensurate xenon/graphite

Calculations of the properties of monolayer xenon/graphite for temperatures up to its triple point at 100 K are reported. The average lattice constant and orientational epitaxy angle for the monolayer solid are evaluated along its (two-dimensional) sublimation curve. The incommensurate rotated lattice approaches the incommensurate aligned configuration as the melting temperature is approached, as in experiments. The calculated temperature, latent heat of melting, and solid-liquid density difference at the triple point agree with experiment. The methods include molecular dynamics simulations for large submonolayer patches of xenon and both self-consistent-phonon and perturbation-variation approximations. An overall quantitative agreement between the simulations, calculations, and experimental data is achieved with an interaction model that includes the spatially periodic xenon-graphite corrugation energy.