Band gap closure and metallization of molecular solid hydrogen

We present electronic-structure calculations for molecular solid hydrogen with emphasis on the study of the metallization via band overlap. Both orientationally ordered and randomly oriented molecules in h.c.p. arrangements are considered. It is found that orientational order favors a smaller band gap and thus metallization. This result is consistent with the observed discontinuity in the vibron frequency if it is assumed that an order-disorder transition occurs simultaneously with metallization.