A thermodynamic model of the rotational phase transition in solid ${\mathrm{C}}_{60}$ is presented. The phase transition which appears at 257 K is a first-order phase transition in which a competition occurs between entropy gain by rotation and energy gain by intermolecular attraction. The anomaly in the specific heat, and the entropy and enthalpy changes observed at the critical temperature are well reproduced in the present numerical results.

• Received 18 August 1993

DOI:https://doi.org/10.1103/PhysRevB.49.2143