The role of the dissipative and random forces in the calculation of the pressure of simple fluids with dissipative particle dynamics

摘要

The role of viscous forces coupled with Brownian forces in momentumconserving computer simulations is studied here in the context of theircontribution to the total average pressure of a simple fluid as derived fromthe virial theorem, in comparison with the contribution of the conservativeforce to the total pressure. The specific mesoscopic model used is the oneknown as dissipative particle dynamics, although our conclusions apply tosimilar models that obey the fluctuation dissipation theorem for short rangeinteractions and have velocity dependent viscous forces. We find that theaverage contribution of the random and dissipative forces to the pressure isnegligible for long simulations, provided these forces are appropriatelycoupled and when the finite time step used in the integration of the equationof motion is not too small. Finally, we study the properties of the fluid whenthe random force is made equal to zero and find that the system freezes as aresult of the competition of the dissipative and conservative forces.