Statistical mechanical calculation of surface properties of simple liquids. IV. Molecular dynamics

For Pt. III see ibid., vol.4, 2433 (1971). A two dimensional molecular dynamics simulation of the liquid-vapour interface of argon at the triple point yields a strongly oscillatory density profile. It is found that the dynamical properties in the transition zone show quasicrystalline characteristics normal to the liquid surface. The velocity autocorrelation indicates phonon lifetimes of up to 5*10-12 s, and the spectral density shows discrete peaks in the vibratory region indicative of a simple lattice structure. On the other hand, the existence of low frequency diffusive modes is evidenced by the nonzero value of the function in the limit omega to 0. Two diffusion constants for motions normal and parallel to the surface are obtained and these are discussed in terms of a jump-diffusion model.