Thermodynamic relations in a driven lattice gas: numerical experiments.

We explore thermodynamic relations in nonequilibrium steady states with numerical experiments on a driven lattice gas. After operationally defining the pressure and chemical potential in the driven lattice gas, we confirm numerically the validity of the integrability condition (the Maxwell relation) for the two quantities whose values differ from those for an equilibrium system. This implies that a free-energy function can be constructed for the nonequilibrium steady state that we consider. We also investigate a fluctuation relation associated with this free-energy function. Our result suggests that the compressibility can be expressed in terms of density fluctuations even in nonequilibrium steady states.