Molecular dynamics simulation of solid C60 under progressively raised pressure

Recent molecular dynamics investigations have shown that C 60 fullerites can be investigated by means of simple potentials and few calculations have focused on the pressure dependence of thermodynamic properties and the induced order-disorder phase transition. The aim of this work is to perform molecular dynamics simulation of the C 60 crystal lattice in the face centred cubic structure under progressively raised pressure, to illustrate the limits of the crude pseudo atom approach and the validity of the potential in the rigid molecule, when seeking for possible phase transitions. For that purpose, several thermodynamic and structural properties are calculated with different potential models in the pseudo atom approach and as a rigid freely rotating C 60 molecule. Calculated properties are compared to experimental data. It will be demonstrated that though the pseudo atom approach is reasonable in the low-pressure region (< 4 kbar), the rigid molecule is in better agreement with experiments depending on the choice of the model potential and the pressure applied. Orientational transition pressures are observed at 5 and 260 K, the distorted lattice and the cell contraction are measured and the density of phonon states is reported at different pressures.