Orientational order phase transition in solid C-60

Abstract

The phonon spectrum and thermal parameters such as specific heat, effective temperature and amplitude of vibration of solid C-60 are studied from ab-initio calculations. The relative orientations between the C-60 balls are taken into account in a sc phase below 261.4K. The same properties are studied above the transition temperature (261.4K) where the balls are randomly oriented in a Sec structure. A difference is found in some of the thermal parameters due to the relative inter-molecular orientation. In particular, the low energy vibrational spectrum (which is separated by a similar to 20meV gap from the intra-molecular spectrum) is changed.