Screening Diffusion of Small Molecules in Flexible Zeolitic Imidazolate Frameworks Using a DFT-Parameterized Force Field

Quantitatively
modeling adsorbate diffusion through zeolitic imidazolate
frameworks (ZIFs) must account for the inherent flexibility of these
materials. The lack of a transferable intramolecular ZIF force field
(FF) for use in classical simulations has previously made an accurate
simulation of adsorbate diffusion in many ZIFs impossible. We resolve
this problem by introducing a density functional theory parameterized
force field (FF) for ZIFs named the intraZIF-FF, which includes perturbations
to the class I force fields previously used to model ZIFs. This FF
outperforms ad hoc force fields at predicting ab initio relative energies
and atomic forces taken from fully periodic ab initio molecular dynamics
simulations of SALEM-2, ZIF-7, ZIF-8, and ZIF-90. We use the intraZIF-FF
to predict the infinite dilution self-diffusion coefficients of 30
adsorbates with molecular diameters ranging from 2.66 to 7.0 Å
in these 4 ZIFs. These results greatly increase the number of adsorbates
for which accurate information about molecular diffusion in ZIFs is
available.