FLUOROPOLYMER FORCE-FIELDS DERIVED FROM SEMIEMPIRICAL MOLECULAR-ORBITAL CALCULATIONS

The van der Waals parameters for Lennard-Jones (6-12) and 6-9 potentia ls and equilibrium geometries for use in molecular mechanics and dynam ics calculations on perfluoroalkanes and polytetrafluoroethylene (PTFE ) have been derived from MOPAC AM1 (Austin model 1) semiempirical calc ulations on the model molecule perfluorohexadecane (PFHD). Parameters derived from MOPAC AM1 energies scaled to yield higher barriers to tor sional motion, as suggested by ab initio results, provide a large tran s 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 intramolecula r geometries and intermolecular packing arrangements are obtained with all parameter sets reported. Copyright (C) 1996 Published by Elsevier Science Ltd.