(572c) First-Principles-Derived Force Fields for CH4 Adsorption and Diffusion in Siliceous Zeolites

Most previous studies on development of force fields for molecules in porous materials focus on prediction of adsorption properties. However, accurately reproducing adsorption data is not sufficient to guarantee the accuracy of other properties such as diffusivities. We demonstrate an approach to develop force fields based on periodic first-principles calculations that can accurately predict both adsorption and diffusion properties in crystalline nanoporous materials using CH₄ in siliceous zeolites as an example. First, multiple dispersion-corrected density functional theory (DFT) methods were tested for describing CH₄ in siliceous chabazite, and two most important configurations that are relevant to CH₄ adsorption and diffusion were investigated. By comparing with the results from high level random phase approximation (RPA) results, DFT/CC (coupled cluster) was found to be the optimum method for force field development. The DFT/CC-derived force fields that accurately predict both adsorption and diffusion of CH₄ in several commonly studied siliceous zeolites are then developed.