3.5 ONIOM Method
143
Physisorption of a water molecule on the modeled graphite (C 96 H 24 ) has been
examined by QM/QM ONIOM2 (B3LYP/6-31 + G*: DFTB-D) finding weak binding
energy 1.8 kcal/mol, where DFTB-D signifies dispersion-augmented density functional tight-binding calculation (Xu et al. 2005). When five water molecules make
a cluster the binding energy becomes 41.7 kcal/mol (Fig. 3.27) compared with the
unbound and unclustered state, signifying there are obviously generated hydrogen
bondings among the water molecules.
It is noted that the ONIOM3 method with a gradual change in the degrees of
precision of the calculation for each layer might be also useful. In Fig. 3.28, the
picture of solvation cluster for Li
+ with propylene carbonate (PC) as the solvent
by the QM/QM/MM ONIOM3 calculation is shown. As the calculation scheme for
each layer is employed, the B3LYP/6-31G: HF/STO-3G: UFF combination. The 1st
layer calculation is performed for only a Li
+ , the 2nd layer for the directly solvated
four PC molecules (see Sect. 4.2; Yanase and Oi 2002 and Ohtani et al. 2010), and
the 3rd layer for surrounding 173 PC molecules. The ONIOM3-optimized solvation
cluster constructs approximately a sphere with the radius of ca. 21.5 Å, signifying the
concentration of electrolyte solution of 0.040 M. Some data concerning this solvation
model is listed in Table 3.4 in which the net charge of Li
+ , averaged net charges of
four oxygen atoms near to the central Li
+ , and Li
+ –O averaged bond orders do not
remarkably change with the addition of the 3rd layer consisting of more than 170 PC
molecules. On the other hand, Li
+ –O bond lengths considerably change according
to the enlargement of the PC solvation cluster. This signifies that the direct solvation
cluster described by the 2nd layer tends to shrink when farther solvent molecules
constructing the 3rd layer are taken into consideration.
Finally, it has generally been pointed out in the ONIOM method that sufficient
preliminary examination is generally recommended to reduce possible mismatching
(From the other angle)
Fig. 3.27 The ONIOM2 calculation result of a supermolecule structure consisting of a modeled
graphite (C 96 H 24 ) and physisorbed water-molecule cluster ((H 2 O) n ; n = 5) above the basal plane.
Atoms expressed by spheres construct the first layer, and wireframe represents the second layer.
Reprinted with permission from Xu et at. (2005). Copyright 2005 American Chemical Society
143
Physisorption of a water molecule on the modeled graphite (C 96 H 24 ) has been
examined by QM/QM ONIOM2 (B3LYP/6-31 + G*: DFTB-D) finding weak binding
energy 1.8 kcal/mol, where DFTB-D signifies dispersion-augmented density functional tight-binding calculation (Xu et al. 2005). When five water molecules make
a cluster the binding energy becomes 41.7 kcal/mol (Fig. 3.27) compared with the
unbound and unclustered state, signifying there are obviously generated hydrogen
bondings among the water molecules.
It is noted that the ONIOM3 method with a gradual change in the degrees of
precision of the calculation for each layer might be also useful. In Fig. 3.28, the
picture of solvation cluster for Li
+ with propylene carbonate (PC) as the solvent
by the QM/QM/MM ONIOM3 calculation is shown. As the calculation scheme for
each layer is employed, the B3LYP/6-31G: HF/STO-3G: UFF combination. The 1st
layer calculation is performed for only a Li
+ , the 2nd layer for the directly solvated
four PC molecules (see Sect. 4.2; Yanase and Oi 2002 and Ohtani et al. 2010), and
the 3rd layer for surrounding 173 PC molecules. The ONIOM3-optimized solvation
cluster constructs approximately a sphere with the radius of ca. 21.5 Å, signifying the
concentration of electrolyte solution of 0.040 M. Some data concerning this solvation
model is listed in Table 3.4 in which the net charge of Li
+ , averaged net charges of
four oxygen atoms near to the central Li
+ , and Li
+ –O averaged bond orders do not
remarkably change with the addition of the 3rd layer consisting of more than 170 PC
molecules. On the other hand, Li
+ –O bond lengths considerably change according
to the enlargement of the PC solvation cluster. This signifies that the direct solvation
cluster described by the 2nd layer tends to shrink when farther solvent molecules
constructing the 3rd layer are taken into consideration.
Finally, it has generally been pointed out in the ONIOM method that sufficient
preliminary examination is generally recommended to reduce possible mismatching
(From the other angle)
Fig. 3.27 The ONIOM2 calculation result of a supermolecule structure consisting of a modeled
graphite (C 96 H 24 ) and physisorbed water-molecule cluster ((H 2 O) n ; n = 5) above the basal plane.
Atoms expressed by spheres construct the first layer, and wireframe represents the second layer.
Reprinted with permission from Xu et at. (2005). Copyright 2005 American Chemical Society