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

Abstract

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.