Ab Initio, Physically Motivated Force Fields for CO₂ Adsorption in Zeolitic Imidazolate Frameworks

Abstract

We present an entirely ab initio methodology, based on symmetry adapted perturbation theory (SAPT), for constructing force-fields to study CO 2 adsorption in nanoporous zeolitic imidazolate frameworks (ZIFs). Our approach utilizes the SAPT energy decomposition to generate physically motivated force fields for the CO 2 -ZIF interaction, with explicit terms representing exchange, electrostatic, induction and dispersion interactions. Each of these terms is fit to the corresponding term in the SAPT energy decomposition, yielding a force field entirely free of empirical parameters. This approach was utilized to construct force fields describing the CO 2 interaction with both ZIF-8 and ZIF-71. In conjunction with our existing CO 2 ÀCO 2 force field, parametrized in a consistent manner, we validate our force fields using grand canonical Monte Carlo simulations and obtain good agreement with the corresponding experimental CO 2 adsorption isotherms. Furthermore, the explicit correspondence between force field terms and fundamental interaction types (dispersion, electrostatics, and induction) allows for an analysis of the underlying physics controlling ZIF gas adsorption that is far more direct and well-defined than with the generic force fields that had been previously utilized to study these systems. As our force fields are free from empirical parameters, these results demonstrate the potential for computationally screening novel ZIFs for flue gas separation applications with near quantitative accuracy.

Genetic Algorithm Optimization of Point Charges in Force Field Development: Challenges and Insights

“…20,21 These simultaneous optimizations of different force field terms can take advantage of extensive training sets that can be easily generated using electronic structure calculations and may include data on the intermolecular interaction energies. [22][23][24][25][26] Moreover, in this approach the fitted interaction energy would implicitly include the polarization effects, even staying within the fixed point-charge force field framework. 9,27,28 However, such simultaneous force field fitting represents a technically challenging multiobjective optimization of the parameters of different physical nature.…”

Improving Predictions of Gas Adsorption in Metal–Organic Frameworks with Coordinatively Unsaturated Metal Sites: Model Potentials, ab initio Parameterization, and GCMC Simulations

“…47,55,57 On the other hand, more sophisticated, physically motivated, but also more complicated, potential energy expressions have emerged. 54,58 The additive terms involved in these intermolecular potentials were fitted explicitly to the decomposition of the corresponding ab initio potential energy whenever and wherever possible. Thus these force fields can be expected to provide a more in-depth interpretation of the physics involved in the system.…”

Recent developments of first‐principles force fields

“…Others used larger model fragment to represent the real materials. These model fragments are large enough to obtain desired details about the interactions, but small enough to implement first‐principles calculations . For a system with periodic structure, the periodic models is useful, as it can retain complete chemical information of the entire framework.…”