Modified Alder-Wainwright model for the velocity autocorrelation function

In a continuous fluid, a spherical volume of atomic size centered at r equals 0 is given an initial velocity v//0. The corresponding velocity field is decomposed into plane waves. Subsequent evolution is described by generalized hydrodynamics linearized in the wave amplitudes. left brace v//0 multiplied by (times) v(r equals 0,t) right brace is taken as a model for the velocity autocorrelation function (VAF), which is obtained as the sum of a longitudinal and a transverse part. Metallic behavior is simulated by a high value of the longitudinal relaxation time, which results in an oscillatory long-time tail of the VAF. Transverse viscoelasticity gives a large contribution to the negative part of the VAF.