Cage Occupancies in Nitrogen Clathrate Hydrates from Monte Carlo Simulations

Comparisons of Gibbs ensemble Monte Carlo simulations with experimental data for the cage occupancies in N-2 clathrate hydrates are performed to assess the accuracy of such simulations, to refine the effective potentials employed, and to help interpret recently measured large cage over small cage occupancy ratios. Different sets of interaction potentials for N-2-N-2, N-2-H2O, and H2O-H2O interactions are considered. Some of them fail to reproduce the known experimental fact that some large cages are doubly occupied at 273 K and high pressures. The best agreement between simulations and experiments is obtained when using a new N-O interaction potential derived in this work by averaging an ab initio potential energy surface for the N-2-H2O dimer.