POTENTIAL-ENERGY SURFACE AND ORIENTATIONAL DISORDER IN SOLID FULLERENE C-60

The polymorphism and molecular disorder in crystalline C-60 have been studied by modelling the optimum packing of fullerene molecules by the atom-atomic potential method. The study includes the calculation of minima and saddle points of the potential energy surface with sorting out of the most common space symmetry groups. Two models of intermolecular potential for C-60 have been checked, one of which assumes effective charges at the centers of C-C bonds. It has been found that the calculated barrier of reorientations is much lower in the case where the concerted character of rotations of different molecules is taken into account. The model of orientational disorder in the face-centered cubic phase is suggested, which is based on consideration of symmetrically arranged equivalent minima separated by low potential barriers.