Force Fields, Structures, and Properties of Poly(vinylidene Fluoride) Crystals

We report two new force fields for molecular dynamics simulations of poly(vinylidene fluoride), PVDF. The first, MSXX, was obtained with Hartree-Fock calculations of 1,1,1,3,3-pentafluorobutane plus experimental frequencies of the form Ip crystal. The second, the covalent shell model (MSXXS), was developed to also account for polarization. These force fields were used to predict structure and properties of nine stable structures of poly(vinylidene fluoride) crystals including the four experimentally observed forms plus a fifth crystal form suggested by Lovinger. In each case we used the force field to establish that the structure is mechanically stable and to predict cell parameters, elastic constants, dielectric constants, and piezoelectric constants.