Will Diamond Transform under Megabar Pressures?

It is predicted that among the fcc, bcc, hcp, simple cubic, and $\beta$-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 $s{p}^3$ 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.