THEORETICAL DETERMINATION OF THE PRESSURE-DEPENDENCE OF THE ELECTRONIC AND THE OPTICAL-PROPERTIES OF FCC C-60

The electronic, optical, and structural properties of fcc C60 crystal are studied as a function of cell volume by means of first-principles local-density calculations. The calculated equilibrium volume, bulk modulus, and the pressure-versus-volume relation are in good agreement with experimental measurements. Changes in the band structure, density of states, bonding pattern, dielectric constant, and optical spectrum with pressure are analyzed and discussed. It is found that the band gap and the absorption threshold energy decrease with increasing pressure while the static dielectric constant increases with increasing pressure. The charge-density map shows that at a pressure of 13 GPa covalent bonding between C atoms in different C60 molecules may form and metallization of C60 at ultrahigh pressure is unlikely. These results are in line with some very recent experimental observations.