Many-body correlations and the cancellation effect in the Green–Kubo time correlation functions for the shear viscosity

Molecular dynamics simulations of the time-correlation functions that appear in the Green–Kubo expression for the shear viscosity are reported for liquid argon over a wide range of densities. The potential part of the microscopic stress tensor is separated into contributions due to the repulsive and attractive branches of the (12/6) Lennard-Jones potential. The separate correlation functions for these parts of the interactions as well as their cross term are further broken down into two-, three- and four-body parts. Each of these shows the same kind of cancellation effect as is found in simulation studies of dipole-induced dipole light scattering. We compare our results to the light scattering findings and find a very consistent picture of the cancellation effect in these time-correlation functions.