  Ji et al. report performing X-ray diffraction on hydrogen compressed to over
250 GPa (https://doi.org/10.1038/s41586-019-1565-9). It is a remarkable
technical achievement. However, the experimental data presented and discussed
in the paper do not support the main conclusion that hydrogen undergoes an
isostructural phase transition and preserves the hexagonal close packed (hcp)
structure up to the highest pressure achieved. The behavior of compressed
hydrogen in the studied pressure range cannot be explained by electronic
topological transition (ETT), as claimed in the paper.
