Effective control of the transport coefficients of a coarse-grained liquid and polymer models using the dissipative particle dynamics and Lowe-Andersen equations of motion

The dynamics of coarse-grained models obtained through iterative Boltzmann inversion [J. Comput. Chem., 2003, 24, 1624] is always faster than that of the parent atomistic models. In this work, the dissipative particle dynamics (DPD) and Lowe-Andersen (LA) equations of motion are applied in coarse-grained simulations to slow down the coarse-grained dynamics. Both methods provide effective friction and both conserve the linear momentum locally, so that they can be used for the calculation of viscosities. Coarse-grained models of liquid ethylbenzene and of short-chain polystyrene melts are studied. Based on the simulation of ethylbenzene at four different temperatures, empirical rules are proposed for choosing the noise strength in DPD or the bath collision frequency in LA dynamics to reproduce the diffusion coefficients of the fully atomistic simulation. The rules developed using the ethylbenzene system are finally tested on the polystyrene melt where they lead to a close reproduction of the experimental diffusion coefficient.