Building large amorphous polymer structures: Atomistic simulation of glassy polystyrene

A technique is presented for generating atomistic models of amorphous polymer structures starting from chain configurations on lattice. The method guarantees Gaussian chain statistics and enables control of chain tacticity and monomer sequence while avoiding severe overlaps between the atoms in the structure. We show that the single polymer chain, which completely occupies the lattice with periodic boundary conditions, is Gaussian with chain statistics equivalent to that obtained for a nonreversing random walk on the cubic lattice. The method enables efficient generation of the chain topology, which can then be populated with specific chemical units. Large models of glassy, atactic polystyrene have been generated, and the effects of system size are examined in terms of calculated X-ray scattering intensities. These results demonstrate the efficacy of this new method for generating more realistic polymer glass structures.