Simple model for the equation of state and orientational order-disorder transition of C60 solid under pressure

A simple model is proposed for the equation of state of Ceo solid under pressure up to similar to 12 GPa and used to analyze selected experimental data. The model consists of a semiempirical modification of the Girifalco potential and is constructed such that it complies with basic experimental results such as the volume change associated with the orientational order-disorder transition observed at 260K under normal pressure. We primarily concentrate on the experimental data of Ludwig et al., which seem the most plausible at low pressure and are the most systematic at high pressure. It is shown that the model can actually be constructed to yield quite well the experimental result in the whole range of pressure.