Probing metastability of carbon at high pressures by predictive first-principles simulations

In spite of extensive experimental and theoretical efforts, the behavior of carbon at extreme conditions is not completely understood. Previous hydrostatic studies demonstrate the stability of diamond and the absence of any other phase of carbon at pressures up to 1 TPa. However, new metastable phases might appear upon uniaxial compression generated by shock waves. We explore unknown metastable phases of carbon under both hydrostatic and uniaxial compressions up to 5 TPa using first-principles crystal structure prediction methods. It is predicted that several new metastable phases appear to survive upon decompression to ambient conditions. The experimental validation of these predictions will open up a new avenue in synthesizing new metastable carbon materials.