Molecular Dynamics Study of Structures and Phase Transitions in C₇₆(D₂) Crystals

Crystal structures of C₇₆ with (D₂) symmetry were calculated by molecular dynamics simulation using reliable potential function. We observed three phases in the crystal structure, a face center cubic (fcc) and two hexagonal (hex1, and hex2). The lattice constants and transition temperatures of fcc and hex2 were good in agreement with experiments. The lattice constants of the crystals were a = 15.50 Å for the fcc and a = 10.93, c = 17.50 Å for the hex2, respectively, at room temperature. The transition temperatures were about 200 K for the fcc, and about 350 and 500 K for the hex2. However any phase corresponding to the hex1 has not been reported in experiments. The lattice constants were a = 10.50, c = 18.42 Å at room temperature and transition temperatures were about 100 and 400 K. The calculated lattice stabilizing energy and density of hex1 were greater than those of hex2.