Model of the orientational phase transition in solid ${\mathrm{C}}_{60}$

A model of the orientation phase transition in pure ${\mathrm{C}}_{60}$ is proposed. Eight discrete states of the fullerene molecule are considered, taking into account the interactions between the pentagons, hexagons, and double bonds of the neighboring molecules. The entropy gain of disorder is in good agreement with the differential-scanning-calorimetry results. The behavior of the order parameters is also in agreement with x-ray and neutron-diffraction measurements. However, the transition temperature obtained in our model with no adjustable parameters is larger than the experimental one.