482
H. Hirao
Fig. 20 QM/MM-derived mechanisms for the reactions in Co-MOF-74 and Mg-MOF-74
(Reprinted with permission from [87]. Copyright 2018 American Chemical Society)
tions. The QM/MM calculations were able to show that the side-on geometry is more
stable than the end-on geometry for the ferric superoxide species. The experimentally
determined binding energy between O 2 and Fe-MOF-74 was also well reproduced.
We have also developed our own methods for rapid force-field parameterization,
which we call partial Hessian fitting (PHF), full Hessian fitting (FHF), and internal
Hessian fitting (IHF) [94, 95] (Fig. 22). We formulated these methods in a way
that minimizes the deviation between MM- and QM-calculated Hessian elements
without going through iterative deviation-minimization processes. These Hessian
fitting schemes performed very well in determining force-constant parameters for 23
different molecules including three secondary building units of MOFs, but in general,
the best performance was obtained with IHF, followed by PHF and then FHF. We