A space-time coarse-grained model for particle simulations of soft matter

C.C. Liew, M. Mikami
Research Institute for Computational Sciences (RICS), AIST, JP

Keywords: soft matter, coarse-grained model, dissipative particle dynamics, simulation

Abstract:
We have developed a series of particle models that are consistent in phase behavior at various space-time coarse-grained levels based on three coarse-graining procedures: Grouping (Gp) for monomer or segment of molecules, Packing (Pk) for grouping of small molecules, and Time-averaging (Ta) for effective potential (Ueff(r)) between two groups of particles over a finite time-span. To adopt these procedures, we have devised a gsoft-attractive-and-repulsiveh potential model, which has an adjustable hardness parameter (beta) and a smooth cut-off (rcut). When beta=6, the function is very similar to LJ(12-6) model, and a series of the new models with beta<5.0 could analytically represent time-coarse-grained Ueff(r) at various time-spans. A model with beta=3.0, analytically represents Ueff(r) over a long time-span, gives excellent energy-conservation with a very long time-step (dt*=0.02) in comparison to LJ (dt*=0.004). Combining the new model with dissipative particle dynamics (DPD) method allows us to retain the phase behavior and dynamics properties of underlying molecular systems for large-scale simulations of soft-matter. As a demonstration, we have performed DPD simulations of surface-induced nanopattern of diblock copolymer film. We found that the simulated structure resembled those pattern observed in experiment of a symmetric PS-b-PMMA thin film on SiOx substrate.

NSTI Nanotech 2003 Conference Technical Program Abstract