  A recent experimental study of the metallization of hydrogen tracked the
direct band gap and vibron frequency via infrared measurements up to ~425 GPa
[P. Loubeyre et al., Nature 577, 631 (2020)]. Above this pressure, the direct
gap has a discontinuous drop to below the minimum experimentally accessible
energy (~0.1 eV). The authors suggested that this observation is caused by a
structural phase transition between the C2/c-24 molecular phase to another
molecular phase such as Cmca-12. Here, through ab initio calculations of
pressure dependent vibron frequency and direct band gap, we find that the
experimental data is consistent with the C2/c-24 phase up to 425 GPa, and
suggest that this consistency extends beyond that pressure. Specifically, we
find that qualitative changes in the band structure of the C2/c-24 phase lead
to a discontinuous drop of the direct band gap, which can explain the observed
drop without a structural transition. This alternative scenario naturally
explains the absence of hysteresis in the measurements.
