Theoretical Investigation On The Structure And Stability Of Clathrate Hydrates H₂-(H₂O)₁2

The clathrate hydrates is made up with the host water cage which is linked byhydrogen-bonded and guest gas molecules . At present, more and more attention havepaid on the use of storing and transporting by the clathrate hydrates for H2.In this paper, the theoretical basis is ab initio method of molecular orbit al theory,the method is self-consistent field and electronic structure calculations, investgatingthe structure and stability about water cage cluster (H₂O)₁₂ and the possibility of theguest H2 molecular capturing and escaping by the host water cage at HF, MP2,CCSD(T) and DFT level with 6-311++G** basis set.Investigate the Bonding mechanism and stability at B3LYP/6-311++G** levelemphasizely, and analysis the geometry, dissociation energy and interaction betweenmoleculars and so on. The result indicated the interaction between non-neighborsmoleculars lead to shrinkage for water cage cluster(H₂O)₁₂.At the basic of the study about the water cage (H₂O)₁₂, meantime studying thestructure and stability of the clathrate hydrates H2-(H₂O)₁₂. To analyze the respectivefeature of the clathrate hydrates, the result indicate that the weak interaction existsbetween the host water cage and the guest H2 molecules .So the stability of theclathrate hydrates H2-(H₂O)₁₂ is stronger than the water cage (H₂O)₁₂ at normaltemperature and pressure.At the basic of the structure and stability of clathrate hydrates, open questions inthe study are whether the H2 guest molecules can migrate between the clathrate cagesand whether H2 is released from the clathrate once it is formed. Electronic-structurecalculations are used to estimate the energy barriers to the escape of H2 guestmolecules from the cages of the clathrate hydrates. We have calculated theone-dimensional energy profile towards to the H2 molecules moving from the cagecenter through the center of hexagonal faces. The energy barriers calculated at theMP2 level with the 6-311G* basisi set are 2.751kcalmol-1. The energy barriers areused to estimate the escape rates from the cage, tunneling contributions to the escaperates are also considered at the same time. These studies indicate that H2 can migratethrough clathrate hydrates and that kinetic considerations can be very important indetermining the structure and H2-storage capacity of clathrate hydrates.