Carbon dioxide occupancies inside ice XVII structure from grand-canonical Monte Carlo simulation

Clathrate hydrate is a promising material that can be used to trap the carbon dioxide (CO2) as a mean for the greenhouse-gas emission control. A compromise between experimental findings and density functional theory calculations was recently made to determine the occupancy of the newly reported CO2 clathrate hydrate of ice XVII structure. In this work, a hybrid isobaric Grand-Canonical Monte Carlo simulation is performed as a direct approach to determine CO2 occupancy inside ice XVII structure. The simulation results show that the CO2-to-water ratio starts at about 1:3.55 under lower pressure and ends at about 1:4 under high pressure. The potential energy of CO2-water interaction as a function of CO2 molecule displacement inside the voids shows a cage-like character, and the orientation of CO2 molecules inside the spiral void is shown to be well-ordered. The simulation results support the experimental observation and provide molecular insight into the structure of CO2 molecules inside the ice XVII structure.