On the simulation of plastic crystals of n-alkanes with an atomistic model

The structure and the dynamics of the rotator phase RI of nonadecane (C19H40) are investigated by Molecular Dynamics simulation on the basis of a model which treats all atoms explicitly. The study of such anharmonic solid phase of flexible molecules where rotational, longitudinal and intramolecular disorder coexist is a real challenge for simulations with a realistic potential. We test the stability of the overall crystal structure by monitoring X-ray patterns and we compare our analysis of the single molecule dynamics with the existing quasi elastic neutron spectroscopy predictions. This comparison shows correct trends of our model system but the reorientational freedom of individual molecules seems to be too large. These calculations illustrate the need for large system sizes when investigating layered structures of chain molecules.