Stability and Reactivity of Methane Clathrate Hydrates: Insights from Density Functional Theory

The sI methane clathrate hydrate consists of methane gas molecules encapsulated as dodecahedron (512CH4) and tetrakaidecahedron (51262CH4) water cages. The characterization of the stability of these cages is crucial to an understanding of the mechanism of their formation. In the present work, we perform calculations using density functional theory to calculate interaction energies, free energies, and reactivity indices of these cages. The contributions from polarization functions to interaction energies is more than diffuse functions from Pople basis sets, though both functions from the correlation-consistent basis sets contribute significantly to interaction energies. The interaction energies and free energies show that the formation of the 512CH4 cage (from the 512 cage) is more favored compared to the 51262CH4 cage (from the 51262 cage). The pressure-dependent study shows a spontaneous formation of the 512CH4 cage at 273 K (P ≥ 77 bar) and the 51262CH4 cage (P = 100 bar). The reactivity of the 512CH4 cage is similar to that of the 512 cage, but the 51262CH4 cage is more reactive than the 51262 cage.