Liquid-Liquid Phase Transformation in Carbon

A first order phase transition is found in liquid carbon using atomistic simulation methods and Brenner's bond order potential. The phase line is terminated by a critical point at 8801 K and 10.56 GPa and by a triple point on the graphite melting line at 5133 K and 1.88 GPa. The phase change is associated with density and structural changes. The low-density liquid is predominantly sp bonded with little sp3 character. The high-density liquid is mostly sp3 bonded with little sp character. This is the first nonempirical evidence of a liquid-liquid transition between thermodynamically stable fluids.