Evidence for a pronounced local orientational order in the high temperature phase of C60

Mechanical properties of solid C(60) studied with density functional tight binding method augmented by an empirical dispersion term

The bulk modulus of solid fcc C(60) was calculated with a density functional tight binding method, augmented by an empirical van der Waals force. The predicted modulus of 9.1 GPa is in good agreement with the experimental measurements. We found that the geometric structures of C(60) molecules in the solid fcc phase are considerably changed under strong compression, due to variations in the type of hybridization of carbon atoms. We also observed a reduction of the HOMO-LUMO gap under compression which is attributed to the overlap of π orbitals from neighboring C(60) molecules. Finally, we showed that the dispersion energy correction in the adopted scheme plays an essential role for the quantitative description of the weakly bound C(60) solid.