Atomistic Modeling of Methane and Carbon Dioxide Structure I Gas Hydrates under Pressure: Guest Effects and...

Gas hydrates are potential candidates in future energy sources while simultaneously providing structures with extensive applications in carbon capture and storage, gas transport, and important separation processes. Prior research in the field considers the dynamics of the water molecule backbone, in particular. We investigated the pressure-enthalpy landscape and mechanical stability envelope of sI methane and carbon dioxide hydrates simulated using DFT. We investigated the effect of revPBE + DFT-D2 and SCAN + rVV10 and their treatment of the exchange-correlation interactions. We examined the zero-pressure material properties, finding that revPBE comparatively underbinds the interactions, causing more flexible structures with large equilibrium volumes. Under pressure, the carbon dioxide molecule was found to align itself parallel to the hexagonal faces of the large cage despite the functional used. Additionally, the property differences are caused by the ability of the carbon dioxide molecule to rotate and disperse the changes in the energy landscape in ways that methane molecules cannot. This computational methodology describes the elastic stability of gas hydrates, marginal stability, and critical differences across important molecular interactions, confirming experimentally observed restrictions in guest molecule rotations and novel pressure behaviors under hydrostatic loads.