Energy flow in thermostatted non-equilibrium molecular dynamics simulations

Energy transfers between internal kinetic and potential energy reservoirs in a simple liquid are studied by setting the temperature of one energy reservoir to a different value from that of the others and computing the resultant energy flows. In the first set of simulations, the x-directional kinetic temperature was artificially raised above the other five, and in the second, the x-directional configurational temperature was artificially raised above the other five. In both cases, external energy flows balanced, but unexpected energy flows between different directional components of the potential energy were observed. Additional simulations showed that these energy flows occurred regardless of the arrangement of thermostats imposed on the six degrees of freedom and the addition of shear. Heat flow between degrees of freedom that were ostensibly at the same temperature was anomalously observed. It was concluded that a different breakdown of the contributions to the configurational energy that is consistent with the definition of the directional configurational temperatures is required.