Thermostat for non-equilibrium multiparticle collision dynamics simulations

TL;DR

This paper compares three thermostats in multiparticle collision dynamics simulations, showing that the Maxwell-Boltzmann based thermostat best maintains correct velocity distributions and thermodynamic properties under non-equilibrium conditions.

Contribution

The study evaluates and compares the effects of three thermostats on non-equilibrium MPC fluid simulations, recommending the Maxwell-Boltzmann approach for accurate velocity distributions.

Findings

All thermostats preserve flow profiles and local temperature.

Viscosity measurements agree with theoretical predictions.

MBS thermostat closely resembles an isothermal ensemble.

Abstract

Multiparticle collision dynamics (MPC), a particle-based mesoscale simulation technique for com- plex fluid, is widely employed in non-equilibrium simulations of soft matter systems. To maintain a defined thermodynamic state, thermalization of the fluid is often required for certain MPC variants. We investigate the influence of three thermostats on the non-equilibrium properties of a MPC fluid under shear or in Poiseuille flow. In all cases, the local velocities are scaled by a factor, which is either determined via a local simple scaling approach (LSS), a Monte Carlo-like procedure (MCS), or by the Maxwell-Boltzmann distribution of kinetic energy (MBS). We find that the various scal- ing schemes leave the flow profile unchanged and maintain the local temperature well. The fluid viscosities extracted from the various simulations are in close agreement. Moreover, the numerically determined viscosities are in remarkably good agreement with the respective theoretically predicted values. At equilibrium, the calculation of the dynamic structure factor reveals that the MBS method closely resembles an isothermal ensemble, whereas the MCS procedure exhibits signatures of an adi- abatic system at larger collision-time steps. Since the velocity distribution of the LSS approach is non-Gaussian, we recommend to apply the MBS thermostat, which has been shown to produce the correct velocity distribution even under non-equilibrium conditions.