Development of AMBER-compliant transferable force field parameters for polytetrafluoroethylene

Abstract

New transferable parameters for polytetrafluoroethylene (PTFE) compatible with the Assisted Model Building with Energy Refinement (AMBER) force field were developed by including many conformational states to improve accuracy. The Austin–Frisch–Petersson functional with dispersion hybrid density functional theory, advantageous for treating dispersion, was used to obtain quantum mechanical reference data. The restrained electrostatic potential method was used to compute the partial charges. The bonds, angles, and dihedral parameters were obtained via Paramfit software fitted to quantum mechanical data. The optimization of van der Waals parameters was obtained in the condensed phase through molecular dynamics simulations and the simplex method. These parameters were transferred to various molecular weights of PTFE assembly systems to calculate the density, radial distribution functions, power spectrum, and specific heat capacity. The highest percent error in density was 1.4% for the modeled PTFE ensembles. The calculated vibrational spectrum peaks closely matched experimental peaks with a maximum wavenumber deviation of 19 cm⁻¹. The highest percent error to specific heat capacity was 5%. These results represent a significant improvement over pre-existing potentials in the literature and provide parameters that can be used to model PTFE in many existing simulation codes.