New approach for the generation of initial configurations suitable for molecular dynamics studies of glassy polymers

Initial configurations suitable for molecular dynamics runs are usually assembled according to random values for the torsional angles of the molecules, and thus representing unrealistic conformations of the polymeric chains. In general, this would be acceptable if the system is allowed to run for periods of time long enough for the molecule to fully relax. However, in the current state of molecular dynamics runs, the 3D-periodic systems are usually allowed to run for 100 ps, which is too short for the polymeric system to relax. Alternatively, traditional rotational isomeric state approximation (RIS) could be used to generate the initial configurations of the polymeric chains. Unfortunately, RIS does not take into account the possible segment–segment overlap between atoms comprising the polymeric chains. In this work, we investigate the possibility of using the rotational isomeric state approximation to properly construct the initial configuration of 3D-periodic systems, without allowing any segment–segment overlap. In order to ensure that these configurations represent realistically the polymeric system, attempts were made to test the configurational properties of these systems against those determined experimentally. Further, these configurations were used to perform subsequent molecular dynamics runs in order to elucidate the effect of the molecular weight of poly(vinyl chloride) and temperature on some of the important thermodynamic properties such as self-diffusion coefficient, thermal pressure coefficient, heat capacity and dielectric constant.