FULL TIME DEPENDENCE OF THE VACF IN CA-FLUIDS: THEORY AND SIMULATIONS

The velocity autocorrelation function (VACF) in a 1-D 5-bits model, the 2-D FHP-III model and the quasi 3-D FCHC model are investigated using mode coupling theory accounting for finite size corrections and for all possible pairs of hydrodynamic modes. This extended mode coupling theory describes the molecular dynamics data of Frenkel c.s. quantitatively from about three mean free times on. For times upto two mean free times the M.D. data agree with the predictions from the Boltzmann approximation. However, in the quasi 3-D model, the M.D.-results exhibit unexplained deviations in the early stages from the Boltzmann values and in the intermediate stage from those obtained with the extended mode coupling theory.