A Transferable Force Field for Predicting Adsorption and Diffusion of Small Molecules in Alkali Metal Exchanged Zeolites with Coupled Cluster Accuracy

We present a transferable force field for small adsorbates (CH4, CO2, O-2, and N-2) in alkali metal (Li, Na, K, Rb, and Cs) exchanged zeolites. The fitting procedure is based on adsorbate-adsorbent interaction energies obtained from periodic density functional theory calculations and corrected using coupledcluster methods applied to small clusters. The fitting approach aims at accurate prediction of both adsorption and diffusion properties by using sets of configurations that sample adsorption sites and intracrystalline hopping transition states. The quality of the force field is assessed for a wide range of adsorbates in zeolites with different chemical composition and topologies, showing good agreement between theoretical predictions and experimental measurements of adsorption and diffusion.