Molecular dynamics study of the stability of methane structure H clathrate hydrates

Molecular dynamics simulations are used to study the stability of structure H (sH) methane clathrate hydrates in a 3x3x3 sH unit cell replica. Simulations are performed at experimental conditions of 300 K and 2 GPa for three methane intermolecular potentials. The five small cages of the sH unit cell are assigned methane guest occupancies of one and large cage guest occupancies of one to five are considered. Radial distribution functions, unit cell volumes, and configurational energies are studied as a function of large cage CH4 occupancy. Free energy calculations are carried out to determine the stability of clathrates for large cage occupancies. Large cage occupancy of five is the most stable configuration for a Lennard-Jones united-atom potential and the Tse-Klein-McDonald potential parametrized for condensed methane phases and two for the most stable configuation for the Murad and Gubbins potential.