Simulation studies of shear viscosity time-correlation-functions

Computer simulations of the Green–Kubo time-correlation-functions (tcfs) for the shear viscosity are reported for argon (Lennard-Jonesium) at several state points. The principal function of interest is the contribution that involves the intermolecular forces. This particular tcf is the sum of a two-body, a three-body, and a four-body term. The time-dependencies and magnitudes of these individual tcfs have been evaluated over a wide range of density at 151 K and for a single state point near the argon triple point. It is shown that all of these component tcfs are significant; that their time-dependencies at moderately short times are quite different from one another; and that the individual functions display pronounced long-time-tails at high density. However, a tail does not appear in the total tcf because of cancellation in the summation. That is, the long-time-tails appear in the partial tcfs in the ratio 2-body:3-body:4-body=1:−2:1.