Prediction of Adsorption and Diffusion Properties of CH4 in Zeolites Using Force Field Derived from DFT-CC Methods

Molecular simulations like Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) are widely used to predict adsorption isotherms, heat of adsorption, and diffusion of adsorbate molecules in porous materials like zeolites. The accuracy of such predictions depends mainly on how accurately Force field represents adsorbate-zeolite interaction. For such simulations, either off-the-shelf force fields (FF) or adsorption fitted force fields are typically used. Developing force fields (FFs) from first principle methods is a powerful approach to developing transferrable FFs that improve upon these approaches. We have developed a transferrable force field for CH₄-zeolite interactions using the DFT-CC method. Here we first developed Coupled-Cluster (CC) corrections for CH₄-zeolite interactions using high level computational chemistry. The DFT-CC method adds corrections to DFT interaction energies to make them closer to CCSD(T) energies. We also tested other DFT methods, finding that PBE-D2, PBE-D3, and VDW-DF2 overestimate adsorption isotherms while the recently developed VDW-DF-CC method underestimates adsorption isotherms. We have applied our newly developed force field to obtain diffusion properties of CH₄ in silica-zeolites.