High Temperature Raman analysis of Hydrogen Phase IV from Molecular Dynamics

TL;DR

This study uses advanced molecular dynamics simulations to analyze phase IV of solid hydrogen, revealing the importance of uncorrelated rotations for Raman spectra and proposing a revised phase diagram.

Contribution

It introduces larger simulation cells and k-sampling to better understand hydrogen phase IV and suggests a new candidate phase at higher pressures.

Findings

Uncorrelated hexagonal rotations are necessary for accurate Raman spectra.

No evidence of proton diffusion or layer fluctuations in large simulations.

Proposes a revised phase diagram for hydrogen under high pressure.

Abstract

We extend our previous studies on phase IV of solid hydrogen by employing larger cells and k-sampling. We show that uncorrelated hexagonal rotations in the weakly bounded G"-layers are needed to account for the experimentally measured Raman spectrum. In large simulations we find no evidence of proton diffusion or layer fluctuations, which we believe are the result of finite size effects. In calculations at higher pressures (above 400 GPa) we identify a new possible candidate for phase IV. We, finally, proposed a revised phase diagram based on our previous and present results.