HARMONIC MODES IN A HARD-SPHERE FLUID

The velocity time correlation function of a hard sphere fluid has been calculated using a generalized Langevin formulation of kinetic theory . When the memory function is approximated by its zero time value, the Langevin equation describes an overdamped harmonic oscillator in whic h the damping term arises from Enskog (uncorrelated collision) frictio n and the oscillator frequency arises from three body correlated colli sion sequences. For very high density fluids, the velocity time correl ation function is in good agreement with molecular dynamics simulation s on hard sphere fluids and the vibrational frequency is in close prox imity to the Debye frequency of argon.