Fluoropolymer force fields derived from semiempirical molecular orbital calculations

The van der Waals parameters for Lennard-Jones (6-12) and 6-9 potentials and equilibrium geometries for use in molecular mechanics and dynamics calculations on perfluoroalkanes and polytetrafluoroethylene (PTFE) have been derived from MOPAC AM1 (Austin model 1) semiempirical calculations on the model molecule perfluorohexadecane (PFHD). Parameters derived from MOPAC AM1 energies scaled to yield higher barriers to torsional motion, as suggested by ab initio results, provide a large trans barrier and stronger intermolecular attractions, which will probably be important for dynamics investigations into the nature of the solid-state phase transitions and helical defects. Reasonable intramolecular geometries and intermolecular packing arrangements are obtained with all parameter sets reported. Copyright (C) 1996 Published by Elsevier Science Ltd.