Possible high-pressure phase of diamond

We theoretically investigate a hypothetical ${\mathrm{sp}}^3$ form of diamond carbon with 16 atoms per unit cell. It contains fivefold rings as a possible result of fullerene transformation under pressure and could be a stable phase of diamond at high pressure. We have calculated the ground-state structure, the cohesive energy, the bulk modulus, and the electronic density of states by means of tight-binding molecular-dynamics and density-functional total-energy calculations. Finally we have compared the phonon spectra at $\Gamma$ and the Raman spectra to existing Raman data for a possible noncubic phase of diamond.