Phase transitions of carbon at extreme conditions

An accurate phase diagram of carbon at extreme pressures and temperatures is of critical importance for constructing interior models of carbon-rich exoplanets as well as for designing  ablation capsules for inertial confinement fusion experiments. However, stability of diamond and possible transitions to other high-pressure carbon phases above 1 TPa are a matter of debate. We investigate the phase diagram and phase transitions of carbon materials in both crystalline and amorphous forms at high temperatures and pressures using machine-learning molecular dynamics (MD) simulations. The MD simulations explain extreme metastability of diamond well beyond the region of its thermodynamic stability and predict experimentally viable synthesis pathways of elusive BC8 high pressure phase of carbon.