). Second, we constructed a library of Ni(PyC-X) 2 crystal structure models by appending a functional group X (for each X in Fig. ) on the PyC ligand of the parent Ni(PyC) 2 MOF; then, we optimized the geometry using DFT calculations. Finally, we used molecular simulations to predict the Xe, Kr, and Ar Henry coefficients and dilute selectivities in each Ni(PyC-X) 2 MOF in the library. Our screening predicted that several functional groups X would enhance the Xe/Kr selectivity and Xe Henry coefficient of the parent MOF (see Fig.