Robust, Transferable, and Physically Motivated Force Fields for Gas Adsorption in Functionalized Zeolitic Imidazolate Frameworks

We extend our existing methodology for generating physically motivated, tailored ab initio force fields via symmetry-adapted perturbation theory (SAPT). The revised approach naturally yields transferable atomic exchange, charge penetration, and dispersion parameters, facilitating the creation of versatile, optimized force fields; this approach is general, applicable to a wide array of potential applications. We then employ this approach to develop a force field, "ZIF FF", which is tailored to accurately model CO2/N-2 adsorption in zeolitic imidazolate frameworks (ZIFs). In conjunction with our previous "SYM" force field used to model adsorbate-adsorbate interactions, we compute adsorption "isotherms for both CO2 and N-2 in nine different ZIFs, yielding results that are in excellent accord with the corresponding experimental results. We find that ZIF FF accurately predicts isotherms for three different topologies of ZIFs (RHO, SOD, GME) and reproduces gas adsorption trends for varying functionalization across an isoreticular series of ZIFs of the GME topology. Because ZIP FF is free of empirical parameters, it presents the opportunity for computationally screening novel ZIFs that have not yet been synthesized and/or characterized.