Abstract: In an attempt to probe the influence of gasmolecule on stability of methane hydrate, geometry optimizations (by B3LYP/6-31G(d,p)) have been performed on different dodecahedral (H2O)20, CH4(H2O)20 and tetrakaidecahedral (H2O)24, CH4(H2O)24 clusters. The result suggested that the CH4(H2O)20 and CH4(H2O)24 clusters were more stable than the (H2O)20 and (H2O)24 clusters by calculating interaction energy andMulliken electron density. It also showed that the CH4 molecule was more important to the stability of methane hydrate. The calculated values of symmetric C—H stretching frequencies of methane were the same as the experimental values in the references. The crystal stability influenced by cage occupancy of hydrate was also simulated by constant-pressure and constant-temperature (NPT) molecular dynamics (MD) method. The result showed that the crystal stability was improved corresponding to the increase of the cage occupancy.

Key words: Methane hydrate, Quantumchemistry, C—H stretching frequency, MD, Stability of gas hydrate