Metallization of molecular hydrogen: Predictions from exact-exchange calculations

We study metallization of molecular hydrogen under pressure using exact-exc hange (EXX) Kohn-Sham density-functional theory in order to avoid well-know n underestimates of band Saps associated with standard local-density or gen eralized-gradient approximations. Compared with the standard methods, the E XX approach leads to considerably (1-2 eV) higher gaps and significant chan ges in the relative energies of different structures. Metallization is pred icted to occur at a density of greater than or similar to 0.6 mol/cm(3) (co rresponding to a pressure of greater than or similar to 400 GPa), consisten t with all previous measurements.