L. Benco et al., Upper limit of the O-H center dot center dot center dot O hydrogen bond. Ab initio study of the kaolinite structure, J PHYS CH B, 105(44), 2001, pp. 10812-10817
Ab initio density-functional (DFT) investigations of the O-H stretching fre
quencies are performed on the kaolinite structure. Four distinct OH groups
form weak hydrogen bonds with O-H . . .O distances between 1.8 and 2.6 Angs
trom. The O-H stretching frequencies, calculated as the Fourier transforms
of the velocity autocorrelation function, show a quasi-linear dependence on
the O-H . . .O distance. Because of the nonspecific character of extremely
weak hydrogen bonds, which are at large distances averaged over several si
milar hydrogen-bond contacts, we anticipate general validity of the frequen
cy vs bond length dependence for all structures with O-H . . .O hydrogen bo
nds. In hypothetical isolated layer, two O-H groups are free of hydrogen bo
nds. The extrapolation of their frequencies indicates an upper limit of sim
ilar to3.0 Angstrom for the O-H . . .O and similar to 4.0 A for the O . . .
O distances. The limiting value of effective hydrogen bond is checked by a
detailed study of the geometry parameters of relaxed structures with contin
uously increased interlayer distance. Discontinuities observed for both the
O-H bond length and the O-H . . .o angles reasonably agree with the value
extrapolated in the frequency vs bond length dependence. The geometrical pa
rameters r(O-H . . .o) = similar to 3.0 Angstrom and r(O . . .o) = similar
to 4.0 Angstrom can thus serve as criteria in assessing the incorporation o
f hydroxyl groups in effective hydrogen bonds.