Pivot Algorithm and Push-off Method for Efficient System Generation of All-Atom Polymer Melts: Application to Hydroxyl-Terminated Polybutadiene
MG Frohlich and TD Sewell, MACROMOLECULAR THEORY AND SIMULATIONS, 22, 344-353 (2013).
Procedures used to generate initial conditions for all-atom molecular dynamics (MD) simulations of amorphous polymer systems are described. The pivot algorithm is applied directly to produce unbranched hydroxyl- terminated cis-1,4-polybutadiene molecules with chain lengths ranging from 8 to 64 monomeric units (32 to 256 carbon atoms), based on the OPLS all-atom force field. The generated molecular configurations are characteristic of (pseudo-) ideal conditions and therefore exhibit the same properties as polymer chains in a melt. We analyze both the mean squared chain dimensions and their distributions in order to validate the correctness of this approach. The chains are efficiently packed into 3d-periodic simulation cells using the push-off method and subsequently equilibrated by standard MD. Together, the pivot algorithm and push-off method provide the means for efficient generation of equilibrated dense polymer melts for multi-million-atom systems.
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