Metallization of molecular hydrogen: predictions from exact-exchange calculations.

We study metallization of molecular hydrogen under pressure using exact-exchange (EXX) Kohn-Sham density-functional theory in order to avoid well-known underestimates of band gaps associated with standard local-density or generalized-gradient approximations. Compared with the standard methods, the EXX approach leads to considerably (1-2 eV) higher gaps and significant changes in the relative energies of different structures. Metallization is predicted to occur at a density of greater, approximately greater than 0.6 mol/cm(3) (corresponding to a pressure of greater, approximately greater than 400 GPa), consistent with all previous measurements.