Phase transition mechanism of hexagonal graphite to hexagonal and cubic diamond: ab initio simulation

We have performed ab-initio molecular dynamics simulations to elucidate the mechanism of phase transition at high pressure from hexagonal graphite (HG) diamond (HD) or cubic (CD). The HG HD is found occur swiftly in very small time 0.2 ps, with large cooperative displacements all atoms. observe that alternate layers atoms slide opposite directions by (1/3, 1/6, 0) and (-1/3, -1/6, 0), respectively, which about 0.7 {\AA} along pm[2, 1, 0] direction, while simultaneously puckering pm0.25 perpendicular a-b plane. CD occurred more complex displacements. In this case, six successive pairs 1/3 [0, 0], [-1, -1, [1, 0, respectively as above. also calculations phonon spectrum pressure, reveal soft modes may facilitate involving sliding layers. zero-point vibrational energy entropy are important role stabilizing up higher pressures (>10 GPa) temperatures than estimated (<6 previous enthalpy calculations.