Dynamic correlations in stochastic rotation dynamics

TL;DR

This paper investigates the dynamic correlations in Stochastic Rotation Dynamics (SRD), providing unbiased measurements of transport coefficients, confirming zero bulk viscosity, and analyzing corrections due to molecular chaos breakdown.

Contribution

It offers the first verification that bulk viscosity is zero in SRD and derives analytical expressions for correlation corrections and collision probabilities.

Findings

Bulk viscosity is zero for SRD.

Transport coefficients match theoretical predictions.

Corrections due to molecular chaos breakdown are quantified.

Abstract

The dynamic structure factor, vorticity and entropy density dynamic correlation functions are measured for Stochastic Rotation Dynamics (SRD), a particle based algorithm for fluctuating fluids. This allows us to obtain unbiased values for the longitudinal transport coefficients such as thermal diffusivity and bulk viscosity. The results are in good agreement with earlier numerical and theoretical results, and it is shown for the first time that the bulk viscosity is indeed zero for this algorithm. In addition, corrections to the self-diffusion coefficient and shear viscosity arising from the breakdown of the molecular chaos approximation at small mean free paths are analyzed. In addition to deriving the form of the leading correlation corrections to these transport coefficients, the probabilities that two and three particles remain collision partners for consecutive time steps are derived analytically in the limit of small mean free path. The results of this paper verify that we have an excellent understanding of the SRD algorithm at the kinetic level and that analytic expressions for the transport coefficients derived elsewhere do indeed provide a very accurate description of the SRD fluid.