A simulation study of the melting of patches of N₂ adsorbed 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.