Molecular dynamics simulation for pressure-induced structural transition from C₆₀ fullerene into amorphous diamond

The pressure-induced structural transition in fcc C$_{60}$ fullerene by shock compression and rapid quenching is investigated by a semi-empirical tight-binding molecular dynamics simulation, adopting a constant-pressure scheme and a method of the order N electronic structure calculation. At first, the process of the amorphization of C$_{60}$ is demonstrated. The simulated results indicated that, in the material fabricated after the quenching, the remaining dangling bonds have a large influence on physical properties, such as, the density and the presence of the band gap at the Fermi level. We have furthermore studied the formation of the short-range order, observed as amorphous diamond. In order to form the amorphous diamond phase, the bonding state of sp$^2$ must be turned into that of sp$^3$. The transition process is seriously influenced from the the external pressure, the temperature, or the presence of hydrogen. The comparison to the pressure-induced structural transition in the graphite is also executed and a brief discussion on the difference in those carbon crystals is given.