Time dependence of phase variables in a steady shear flow algorithm.

We study the periodic time dependence of shear stress that occurs in a low- and a high-density fluid in a molecular dynamics algorithm for simulation of constant shear flow. We present a generalization of the linear response theory for a case when the equilibrium relaxation function and the equilibrium shear stress depend on strain. The predictions of this generalization reveal that the time dependence at low densities is a completely nonlinear effect. At high densities the amplitude of equilibrium oscillations of shear stress with strain is modified by strain-dependent viscosity, causing a decrease in amplitude proportional to shear rate in the linear response regime.