Transferability of CO2 Force Fields for Prediction of Adsorption Properties in All-Silica Zeolites

We present a systematic and comprehensive investigation of available CO2 force fields for their predictions of adsorption properties in 156 geometrically diverse zeolite structures. The comparison reveals that a large discrepancy in the predicted properties, by more than 2 orders of magnitude, may exist. Especially, variation predicted by different force fields appears to be more pronounced for zeolites with more confined pore features, which can be attributed to the repulsive characteristics of force fields. The discrepancy especially impacts zeolites that are deemed to be the best materials for carbon capture and sequestration (CCS), indicating that the predictions on the best materials can drastically differ, based on the choice of force fields. To develop accurate and fully transferable force fields, in this work, we show that the inclusion of adsorption uptake at a high-pressure region (or saturation loading), as well as the diffusion coefficient, can be of utmost importance. These properties can be used as indicators for the repulsive behaviors between gas molecules and the framework. Mixture isotherms have also been identified to be potentially useful for the same purpose. Moreover, we have also demonstrated that interaction energies computed by ab initio methods can be useful references to ensure a newly developed force field is capable of describing the energy surface at an atomic level. Overall, the outcomes of this study will be instrumental to the future development of accurate and transferrable force fields, which is critical for future large-scale computational studies.