On the thermodynamic stability of clathrate hydrates IV: Double occupancy of cages

Multiple occupancy of a single cage of calthrate hydrates was measured using van der Waals and Platteeuw theory. A simple way to calculate the free energy of multiple cage occupancy was proposed and method to apply it to argon clathrate structure II in which a larger cage can be occupied by two argon atoms. The chemical potential of argon was calculated treating it as an imperfect gas, which is crucial to predict accurate pressure dependence of double occupancy expected at high pressure. The results show that the double occupancy dominates over single occupancy when the guest pressure in equilibrium with the calathrate hydrate exceeds 270 MPa.