Towards a computational chemical potential for nonequilibrium steady-state systems

We explore an approach to derive a computable chemical potential analog for thermostatted steady-state systems arbitrarily far from equilibrium. Although our method is not rigorous, it is based on theoretical and numerical evidence and exploits analogies with Widom's method widely used in computer simulations of equilibrium fluids. We obtain two formulas, one for steady states and one for the transient region. Despite being analogous to the equilibrium expression, the steady-state formula can only be used for approximate calculations. Possessing less obvious characteristics, we present representative calculations for the transient approach and discuss its numerical feasibility. [S1063-651X(99)04511-0].