(629d) Ab Initio Carbon Capture in Open-Site Metal Organic Frameworks - Force Field Development and Its Applications

Carbon capture and sequestration (CCS) is a viable strategy proposed to mitigate the negative environmental impacts derived from burning fossil fuels.  Recently, nano-porous adsorbent materials such as metal-organic frameworks (MOFs) have shown to potentially provide a more energy-efficient way to separate CO₂ out of flue gases. In particular, MOFs that possess unsaturated open metal sites are known to interact strongly with CO₂ molecules, and thus emerging as promising materials for the separation applications. However, from the computational point of view, the strong interaction is poorly modeled by common force fields, resulting in underestimation of the adsorption properties of CO₂ in Mg-MOF-74 by as much as an order of magnitude. Accordingly, a systematic methodology has been proposed to generate accurate force fields using high-level quantum chemical calculations¹. In this method, interaction energies of a few selected CO₂ configurations computed by quantum calculations are used to properly map into the force field parameters. In our previous study¹, Møller-Plesset second-order perturbation theory (MP2) with representative small framework fragments was used in the force field development. To facilitate the automation of this methodology as well as resolve the intrinsic discrepancies between cluster and periodic calculations, a methodology based on the periodic density functional theory (DFT) calculations is introduced in this work. The calculated binding geometry and adsorption properties from the DFT-derived force fields show excellent agreements with the ones from DFT calculations and experiments, respectively. Finally, we have also utilized the new DFT-derived force field to study the CO₂ dynamics in Mg-MOF-74 and made connections to our previous study². 

Reference

¹ A. Dzubak, L.-C. Lin, J. Kim, J.A. Swisher, R.  Poloni, S.N. Maximoff, B. Smit, L. Gagliardi, Ab initio carbon capture in open-site metal–organic frameworks, Nat. Chem. 2012 (4), 810-816.

² L.-C. Lin, J. Kim, X. Kong, E. Scott, T.M. McDonald, J.R. Long, J.A. Reimer, B. Smit, Understanding CO₂ Dynamics in Metal-Organic Frameworks with Open Metal Sites, Angew. Chem. Int. Ed. 2013 (52), 4410-4413.