Prediction of Adsorption Properties of Cyclic Hydrocarbons in MOFs Using DFT-Derived Force Fields

We present an extension of previous methods that derive transferable force fields to describe the adsorption of small molecules in zeolites based on density functional theory (DFT) calculations to examine the adsorption of C8 cyclic hydrocarbons in metal-organic frameworks (MOFs). We use our DFT-based force field to predict the adsorption properties of these molecules in MOFs where dispersion governs adsorption properties using grand canonical Monte Carlo (GCMC) simulations. We observe that DFT-derived force fields provide moderately more accurate predictions compared to generic force fields for single-component adsorption in these systems. We find that generic force fields can give qualitative agreement with experiments for binary selectivities, which could eventually be useful for materials screening purposes. We also assess the influence of factors such as framework relaxation due to guest adsorption on these calculations and find that these effects can produce significant changes in the simulated binary selectivities at high loadings. Our methodology will eventually be useful for developing force fields for systems in which generic force fields are known to fail and represent a useful step in understanding and predicting adsorption properties of C-8 hydrocarbons in MOFs.