New Green-Kubo formulas for transport coefficients in hard sphere-, Langevin fluids and the likes

Abstract

We present generalized Green-Kubo expressions for thermal transport coefficients $μ$ in non-conservative fluid-type systems, of the generic form, $μ$ $= μ_\infty$ $+\int^\infty_0 dt V^{-1} \av{I_ε\exp(t {\cal L}) I}_0$ where $\exp(t{\cal L})$ is a pseudo-streaming operator. It consists of a sum of an instantaneous transport coefficient $μ_\infty$, and a time integral over a time correlation function in a state of thermal equilibrium between a current $I$ and its conjugate current $I_ε$. This formula with $μ_\infty \neq 0$ and $I_ε\neq I$ covers vastly different systems, such as strongly repulsive elastic interactions in hard sphere fluids, weakly interacting Langevin fluids with dissipative and stochastic interactions satisfying detailed balance conditions, and "the likes", defined in the text. For conservative systems the results reduce to the standard formulas.