Use of Monte Carlo in calculating the thermodynamic properties of water clathrates

Equilibrium dissociation pressures for monovariant three-phase (icesolid clathrate-gas) systems were predicted for water clathrates with Ar, Kr, Xe, N2, O2, CO2, and CH4 as the guest molecules. A Monte Carlo approach of statistically sampling the states available to the guest molecule inside the host water cage was used to evaluate the configurational properties including the free volume integral. The Lennard-Jones 6–12 potential adequately described the guest-host interaction for monatomic species, for example, Ar, Kr, and Xe, while the nonspherically symmetric Kihara potential with a fixed hard-core geometry was required for polyatomic guests. The simulated motion of the guest within the cell was consistent with the geometrical features of the host lattice.