Electronic Structure Characterization of Molecular Interactions in Clathrate Hydrates

Abstract

Clathrate hydrates are crystalline solids which consist of gas molecules encapsulated in various polyhedral water cages. The formation of these hydrates requires conditions of low temperature and high pressure. These hydrates have potential applications in energy storage, carbon dioxide sequestration, hydrogen storage and biomedical applications. Various molecules such as Ar, Kr, oxygen, nitrogen, carbon monoxide, methane, ethane, propane and carbon dioxide are known to exist in the form of clathrate hydrates. The thesis focuses on the structure, energy, stability, mechanism of formation and spectral properties of cages of various clathrate hydrates using Density Functional Theory (DFT). Some examples are methane, hydrogen, nitrogen and oxygen clathrate hydrates. Methane clathrate hydrates are known to have potential applications as an alternate source of energy due to its abundance. The characterization of interaction energy, thermodynamic stability and vibrational Raman spectra with encapsulation of methane in various cages of clathrate hydrates is presented. The dependence of interaction energies on basis sets and functionals is also discussed. The mechanism of di usion of methane in various cages is characterized using the Climbing Image Nudged Elastic Band method. The activation energy of di usion in these cages and fused cages is also examined. Clathrate hydrates containing hydrogen are potential sources of energy, where addition of tetrahydrofuran reduces the thermodynamic conditions of formation of hydrogen clathrate hydrates. The stability, hydrogen storage capacity and vibrational Raman spectra of multiple occupancy of hydrogen molecules in pure and tetrahydrofuran doped cages of hydrogen clathrate is calculated and compared with experiments. The energy and spectral properties of cages of nitrogen and oxygen clathrate hydrates is also presented. A characterization of methane replacement by carbon dioxide in the cages of clathrate hydrates using Ab initio Molecular Dynamics simulations and an examination of hydrogen clathrate hydrate formation and nucleation is presented as one of the future activities.