Phase diagram of carbon at high pressures and temperatures

We have made a systematic study of solid and liquid phases of carbon over a wide range of pressures and temperatures using first-principles molecular dynamics. Our simulations elucidate three aspects of the phase diagram: (1) the melting of the simple cubic phase at 35--40 Mbar; (2) structural changes in the liquid in the range of 4--10 Mbar; and (3) the melting of the BC-8 phase at {~}22 Mbar. We combine the results of these three investigations to construct a proposed phase diagram for carbon. In particular, we find that above {~}6 Mbar the liquid state has approximately sixfold coordination, and, consequently, that the melting temperatures of the solids in this pressure range tend to decrease with increasing pressure. {} 1996 The American Physical Society.