气体分子对甲烷水合物稳定性的影响

通过B3LYP方法, 在6-31G(d,p)水平下, 分别优化了结构I型甲烷水合物十二面体和十四面体晶穴结构. 结果表明, CH4分子使晶穴的相互作用能降低, 增强了晶穴的稳定性. 计算了晶穴中甲烷分子C—H键的对称伸缩振动频率, 计算结果与实验值相符合. 研究发现CH4分子影响晶穴中氧原子的电荷分布, 从而增强了氢键的稳定性. 通过分子动力学方法研究水合物晶胞中气体分子的占有率对水合物稳定性的影响, 进一步说明气体分子对水合物晶穴稳定性的重要作用.

Influence of Gas Molecule on Stability of Methane Hydrate

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.