Onset of metallization and related transitions in solid hydrogen

The onset of metallization in highly compressed solid hydrogen and a corresponding discontinuity in molecular vibrations have been linked in the literature to band-gap closure in an ordered hcp structure. Extensive first-principles calculations are performed on the energetics and the electronic properties of solid hydrogen, and variations in molecular orientations, bond lengths, and the c /a ratio are explored in detail within an hcp lattice. It is found that the commonly assumed structure is energetically unfavorable, and that lower-energy structures have wider band gaps to much higher density. Implications for the onset of metallization are discussed. (Author)