First principles molecular dynamics study of proton disorder in C1′ phase of H2 hydrate

The proton-disordered and -ordered crystal structures proposed based on X-ray diffraction experiments for the C1′ phase of H2 hydrate were investigated using first-principles (FP) path-integral ring-polymer molecular dynamics (RPMD) simulations. Our simulated Raman spectra obtained from the FP-RPMD trajectories provide unambiguous evidence for static orientational disorder of H2O molecules forming stacked H-bonded rings. This feature is essential to reproduce the characteristics of the observed Raman spectra. Furthermore, the present study shows that van der Waals interactions need to be treated carefully to achieve satisfactory computational results. The findings of this study can help for better understanding of icy materials.