Raman Spectroscopy and Cage Occupancy of Hydrogen Clathrate Hydrate from First-Principle Calculations

Statistically averaged Raman spectra of H, in hydrogen clathrate are calculated by quantum-mechanical calculations and molecular dynamics simulations. The result shows that the H, molecules in the large cages and singly occupied small cages are loosely encaged and the vibrational modes are softened and uncoupled, while those in the doubly occupied small cages are tightly confined, the vibrational modes are strongly coupled, and the frequencies are blue-shifted relative to the free gas. This finding provides important new insights on characterizing the cage occupancy and could inspire innovative experiments for synthesizing the clathrate as a hydrogen storage medium.