Modeling CO2 Adsorption in Zeolites Using DFT-Derived Charges: Comparing System-Specific and Generic Models

For most guest molecules, electrostatic interactions have a non-negligible impact on the adsorption properties of microporous materials, such as zeolites or metal organic frameworks. In force-field-based simulations of adsorption, partial charges located at atomic sites are most commonly used to account for electrostatics. These charges are either derived empirically or obtained from electronic structure calculations. In previous work addressing the adsorption of CO2 in all-silica zeolites, we have used a first-principles approach to derive system-specific charges from density functional theory (DFT) calculations. While this approach has been shown to perform very well, it has the drawback that it requires a separate DFT calculation for every system. In this work, we develop a set of generic charges that reproduces interaction energies from dispersion-corrected DFT calculations equally well as the initial, system-specific set. The performance of this set of charges is then assessed using grand-canonical Monte Carlo simulations of CO2 adsorption and CO2/N-2 mixture adsorption for a total of 24 zeolite frameworks. The results are compared to analogous simulations using the system-specific charges. While the qualitative features are reproduced very well, the quantitative deviations are often non-negligible, amounting to more than 20% in a number of cases. Therefore, the generic charge set can be recommended for screening studies, but system-specific charges should be employed for more detailed investigations.