The Study For Natural-gas Clathrates Hydrates With First-principle Method

Abstract: Geometric, mechanical, acoustic and thermodynamics properties for three common hydrates structures I, II and H were calculated using first-principles. Elastic constants were estimated by fitting Gibbs free energy versus Lagrangian strains. Bulk modulus, Shear modulus, Young's modulus and Poisson's ratio deduced from elastic constants are good agreements to experimental values. The bulk modulus and derivative bulk modulus are also fitted from Birch-Murnaghan equation of states (EOS), and the bulk modulus are in well accordance to results deduced from elastic constants for two cubic clathrates hydrates systems. The longitude and transverse velocity were overestimated by our calculation compared with the experimental results, but reasonable. Appling Debye model, some thermodynamics properties were estimated, including heat capacity, linear thermal expansion, Grüneisen parameter and Debye temperature for cubic structure sI and sII.