Crystal field, orientational order, and lattice contraction in solid C60

A model of the intermolecular potential in solid C60, which is based on Born–Mayer repulsions, van der Waals attractions, and electrostatic multipoles, is presented. The potential is expanded in terms of multipolar rotator functions. The orientation–orientation interaction and the crystal field are calculated. The orientational phase transition to the Pa3̄ phase is studied with the methods of statistical mechanics. The discontinuity of the order parameter at the transition and the temperature evolution of the order parameter are calculated. The lattice contraction at the phase transition is evaluated. The influence of the lattice contraction on the crystal field and on the orientational order is studied.