A Refined Set of Universal Force Field Parameters for Some Metal Nodes in Metal-Organic Frameworks

Metal-organic frameworks (MOFs) exhibit promise as porous materials for carbon capture due to their design versatility and large pore sizes. The generic force field (e.g. UFF and Dreiding) uses one set of Lennard-Jones parameters for each element, while MOFs have a much richer local chemical environment than those used to fit the UFF. When MOFs contain hard-Lewis acid metals, UFF systematically overestimates $CO2$ uptakes within MOFs. To address this, we developed a workflow to affordably and efficiently generate reliable force fields to predict \ce{CO2} adoption isotherms of MOFs containing metals from groups IIA (e.g. Mg, Ca, Sr, Ba) and IIIA (e.g., Al, Ga, In), connected to various carboxylate ligands. This method uses experimental isotherms as input. The optimal parameters are obtained by minimizing the loss function of the experimental and simulated isotherms, in which we use the Multistate Bennett Acceptance Ratio (MBAR) theory can be used to derive the functionality relationship of loss functions in terms of force field parameters.