Density functional theory studies of hydrogen bonding vibrations in sI gas hydrates

Abstract

To analyze the vibrational modes of water and methane in structure I gas hydrates, we constructed a 178-atom supercell with two small cages of type 5 ^12 and six large cages of type 5 ^12 6 ^2 . We applied the density functional theory method to simulate the vibrational spectrum and normal modes of methane hydrates. In accord with our previous studies, we confirmed that two groups of hydrogen bond (H-bond) peaks (at around 291 and 210 cm ^−1 ) in the translational bands come from two kinds of intermolecular H-bond vibrational modes. This is the first investigation of H-bond vibrations in methane hydrates. The partial modes of CH _4 were extracted. We found that the CH _4 phonons in the translational region are below 180 cm ^−1 so that the influence of methane on the H-bond is insignificant. We proposed a new method to decompose gas hydrates via direct application of terahertz radiation to the H-bonds. Herein, we confirmed that CH _4 molecules do not absorb this energy.

Keywords

• hydrogen bonding
• gas hydrates
• phonons
• DFT