Size scalability of Monte Carlo simulations applied to oxidized polypyrrole systems

Abstract

Oxidized polypyrrole (PPy) is a conducting polymer with diverse applications such as supercapacitors, sensors, batteries, actuators, neural prosthetics, among others. PPy is most commonly synthesized for the specific application yielding low molecular weight oligomers that form amorphous polymer matrices. Hence, molecular simulation analyses are challenging. This work generalizes the recently proposed coarse grained force field (CGFF) for halogen oxidized PPy in the condensed phases and introduces a novel implementation of the Monte Carlo (MC) simulation based on the CGFF that enables simulations of polymer systems with more than 100000 particles. The MC implementation utilizes a combination of CPU and GPUs and exploits a numerical approximation based on polynomial piecewise interpolation for the calculation of the CGFF pairwise additive terms. The MC simulations evidence that the oxidized PPy thermodynamic and structural properties are consistent as the system size is scaled up. Predicted properties include density, enthalpy, potential energy, heat capacity, coefficient of thermal expansion, caloric curve, glass transition temperature range, compressibility, bulk modulus, radial distribution functions, and polymer chain characteristics. The oxidized PPy samples display oligomer chain stacking that persists with temperatures up to the glass transition. Simulated properties are consistent with experimental observations when available and predict trends in all other cases.