Directional dependence of the random kinetic energy in planar Couette flow

Non-equilibrium steady state systems do not obey the equipartition theorem in that the distribution of the random kinetic energy among the three directions is not independent of the mechanism which removes the dissipative heat. This becomes important beyond the linear regime because system properties will be functions of the thermostatting mechanism as well. For homogeneous non-equilibrium molecular dynamics simulations, in most of the cases, the simplest synthetic thermostat is used in which, analogously to equilibrium algorithms, the friction coe cient is identical in the x, y and z directions. The simplicity is attractive, but computer simulation results are presented that demonstrate that this may not be the most sensible choice physically.