The temperature in dissipative particle dynamics

The two most popular algorithms for dissipative particle dynamics (DPD) are critically discussed. In earlier papers, the Groot-Warren algorithm with lambda = 1/2 was recommended over the original Hoogerbrugg-Koelman scheme on the basis of a marked difference in their equilibrium temperatures. We show, however, that both schemes produce identical trajectories. Expressions for the temperatures of an ideal gas and a liquid as functions of the simulation parameters are presented. Our findings indicate that the current DPD algorithms do not possess a unique temperature because of the way in which the dissipative and random forces are included. The commonly used large time steps are beyond the stability limits of the conservative force field integrator.