Prediction of Water Adsorption in Copper-Based Metal-Organic Frameworks Using Force Fields Derived from Dispersion-Corrected DFT Calculations

We develop transferable force fields describing water adsorption in copper-based metal-organic frameworks (MOFs) by combining dispersion corrected density functional theory (DFT) calculations and classical atomistic simulations. The DFT-D2 approach was found to give reasonable agreement with high level quantum chemistry results for the interaction between water and CuBTC. A classical force field for water adsorption in CuBTC including Lennard-Jones (LJ), Coulombic interactions, and a water-copper distance-dependent correction term was then developed on the basis of 1200 DFT-D2 calculations that probed the full range of accessible volume in CuBTC via random sampling. Good agreement was obtained between adsorption isotherms predicted with our first-principles-derived force field and experiments. Other commonly used models such as simple combinations of U and Coulomb potentials cannot adequately describe the interaction between water and CuBTC due to the chemical bonding between water oxygen and copper atoms. The transferability of this force field was examined using available adsorption isotherms for water in two structurally distinct copper-based MOFs, CuMBTC (methyl-1,3,5-benzenetricarboxylate) and CuEBTC (ethyl-1,3,5-benzenetricarboxylate), again with reasonably good agreement between calculated and experimental results.