Lattice Dynamical Simulation Of Clathrate Hydrates

Lattice dynamics simulation of ice Hi and clathrate hydrates has been carried out to study the corresponding structural and dynamic properties. Comparisons in PDOS of them were performed and it was found that the spectra resembled each other in both translational and librational regions, which seems to contradict the substantially different lattice structures. Besides, inelastic neutron scattering (INS) carried out in Rutherford Appleton Laboratory (RAL) draw the same conclusion. The resemblance is mostly attributed to the similarity of local oxygen configuration. At the same time, there is anomaly in thermal conductivity through the analysis of the thermodynamic properties of (EO and THF) hydrates and ice In. From 100-270K, the thermal conductivity of hydrates is only fifth that of ice Ih. Therefore, it is significant to make a comparison of the spectra between hydrate and ice Di due to the fact that thermal. conductivity is connected directly with phonon scattering mechanism. Both experimental and calculated vibrational spectra show that the vibrational coupling between guest and host occurs mainly in low-energy band, especially acoustic band (0-15meV), which may be responsible for the anomalous thermal conductivity.On the other hand, a series calculations using LD simulation of different-occupancy noble gas (Helium and Argon) hydrates were carried out to study the interaction in detail between the guest and host with the help of TIP3P potential model, empty hydrate included. Comparisons between the empty and different-occupancy hydrate show that the interaction between the guest and host is not so simple as traditional view. In the thesis, the most important conclusion about the topic is that the small cage and large cage contribute both the high and low energy in acoustic vibrational coupling. It's a mixture. At the same time, an unexpected result is that the energy shift toward high energy against ice Ih in translational region mainly origins from the coupling in large cages. Of course the closing lattice structure of hydrate is a partial contributor. In order to study the stability effect of different-size guests, a comparisonbetween the spectra of Argon and Helium hydrates were carried out. In Helium hydrate, it was found that the coupling between the Helium and large cage is much weaker than that of small cage. Considering the stabilization of gas hydrate, as a result, the interaction in small cages is mainly attributed to the stability of small guest hydrates. If it is suitable for sH hydrate, the result may be used to explain the stability of hydrogen hydrate, which was recently synthesized in laboratory. In order to analyze how different rigid potential models describe the gas hydrate, a LD simulation was performed using BF, TIP3P and TIP4P to calculate the PDOS of methane hydrate. Compared the INS spectra taken from RAL, it was found that all the potentials gave well-separated translational and librational regions. However, all of them can not reproduce the double peaks (about 28 and 37 meV) in optics band due to the lack of hydrogen bond. Finally in order to study thermodynamic inhibition mechanism, the RAL experimental data about the ethanol (CHaCHjOD) hydrate is taken to analyze the interaction between the ethanol and water. It is found that the inhibition occurs as a result of the formation of hydrogen bond between the ethanol and water. It was also found through NMR experiments with methanol hydrate in literature.In the final section, a brief overview is provided about the formation and dissociation mechanism and application (energy resource and geology et al.). An initial understanding of gas hydrate on molecular level is presented through computer simulation (Monte Carlo and Molecular Dynamics), which is fundamentally important to develop the gas hydrate.