STABLE PHASES OF SOLID HYDROGEN AT MEGABAR PRESSURES AND AT ZERO TEMPERATURE

We have explored the stable phases of solid hydrogen by calculating band-theoretical energies in the local density approximation, for the system of oriented molecules at Mbar pressures and at zero temperature. It is shown that the hexagonal-close-packed lattice persists up to approximately 300 GPa with a structure of space group Pca2(1), which has wide band gaps. The subsequent phase is still molecular with a rutile structure with c/a approximately 0.9 which must be conducting. The molecular phase terminates at approximately 600 GPa, where the atomic phase with a planar structure appears.