Stationary nonequilibrium states by molecular dynamics. Fourier's law

Abstract

We have developed a technique to produce stationary nonequilibrium states in a molecular-dynamics system; this method is based on the introduction of stochastic boundary conditions to simulate the contact with a thermal wall. The relaxation times involved in such contact are short enough (\ensuremath{\sim}${10}^{\ensuremath{-}11}$ sec) to make the technique suitable for computer experiments. The method allows the simulation of bulk properties in a system coupled with a heat reservoir and the study of the local thermodynamical equilibrium. Furthermore, it gives a physical description of the heat transfer near a thermal wall. The method has been applied to simulate high thermal gradients in a region of dense fluids ranging from the gas-liquid coexistence line to the freezing line, to check the validity of the linear thermal response (Fourier's law). We have found that the linear region extends at least up to gradients of the order of 1.8\ifmmode\times\else\texttimes\fi{}${10}^{9}$ K/cm for argon. In the bulk region where boundary effects are negligible we have verified the validity of the local equilibrium hypothesis for all simulated gradients.