  There is ample experimental evidence on the existence of several crystalline
phases of C4F8, although they still have been not clearly identified. In this
paper we perform a series of molecular dynamics (MD) simulations using a
partially flexible molecular model, which takes into account the mixing of the
low frequency intramolecular modes and lattice modes. The calculations are
carried on in the constant pressure- constant temperature ensemble and the
algorithm employed allows volume and symmetry changes of the MD sample as a
function of thermodynamic variables. Although several stable crystalline phases
are found, their number is still less than found by experiments.
