A simulation study of the melting of patches of N2adsorbed on graphite

Abstract

The molecular dynamics technique has been used to simulate patches of solid nitrogen adsorbed on the basal plane of graphite. A model of the molecule-surface interaction involving an isotropic site-site interaction predicts a melting transition 9 K below the experimentally observed temperature and leads to an adsorbed liquid patch on melting. By including the anisotropy in the site-site interaction the lateral surface barriers are increased and a site-site potential of the form with γ_A = 0·4, γ_R = -1·05 will reproduce the experimental transition temperature. The nature of the phase above the melting transition cannot be determined with certainty. The simulation does not give a uniform density distribution for the anisotropic model, but we speculate that the spreading of the patch occurs on a time-scale longer than the simulation. There is clear evidence for a periodic density fluctuation in the adsorbed liquid associated with the molecule-surface potential.