It is predicted that among the fcc, bcc, hcp, simple cubic, and β-tin phases, diamond will first transform to the simple cubic phase under a hydrostatic pressure of 23 Mbar. The absence of p electrons in the core causes remarkably strong sp3 bonding in diamond. This stabilizes diamond against the other five phases under high pressures. The study is carried out using ab initio pseudopotential theory within the local-density-functional formalism.

http://dx.doi.org/10.1103/PhysRevLett.50.2006