First-principles phase diagram of carbon at extreme conditions

The accurate phase diagram of carbon at extreme temperatures and pressures is of paramount importance for design of inertial confinement fusion capsules where diamond is used as an ablator material. In spite of intensive experimental and theoretical efforts, there still exist outstanding problems including disagreement between theoretical predictions and experiment. We present results of first-principles molecular dynamics simulations of thermodynamic properties of carbon at high temperatures and pressures, which are performed with the goal of constructing an accurate phase diagram of carbon. To address the issue of accuracy and reliability, a relatively large number of atoms is used for calculation of melting transitions (melt curve) as a function of pressure using two-phase method. We specifically focus on important region of high pressure, high temperature phase diagram where melt line of diamond exhibits a negative slope, while intersecting the melt line of high-pressure bc8 phase at diamond-bc8-liquid triple point.