Decomposition of methane hydrates at high pressure: a density-fuctional theory study

The high pressure properties of methane hydrates have been the subject of intense research in the last decade due to their relevance in geophysics and planetary sciences. Earlier studies have indicated that the compound is remarkably stable under pressure, however a recent report has shown that the compound decomposes into its constituents, ice and methane, above 3GPa. Here, we report the results of density-functional theory calculations and show that methane hydrate is energetically unstable against decomposition above a few GPa. The enthalpy difference between the compound and the constituents reaches a value of 0.45eV per molecule at 80GPa, in favor of the constituents.