Coulomb interactions hydrogen-bonded dimers

In the naphthoic acid crystal (Table 1.1.7), the by far most dominant structure determinant is, as expected, the hydrogen bonded cyclic dimer, A, described by the Pixel approach as a strongly coulombic interaction, while the polarization component supposedly represents the stabilization deriving from the dynamic rearrangement of the electron density - the partial covalent bond character. Next, at a considerable energetic distance, comes a determinant in which the dispersive stacking contribution dominates. The hydrogen bonded dimer is complemented... 

Table 5.3 shows a decomposition of the EFP interaction energy in water-TBA dimers. As expected. Coulomb and exchange-repulsion energies contribute the most to the total hydrogen bonding energy for all of the dimers. The Coulomb energy fraction decreases in... 

Calculations of a similar nature have demonstrated that replacement of both hydrogens of water, yielding dimethyl ether, also has only a minor effect upon the nature of the H-bond in the water dimer. With their polarized basis set, and with inclusion of corrections for BSSE, dispersion, and intramolecular correlation effects, these authors found the first methyl substitution raises the binding energy by 0.5 kcal/mol and the second by 0.6. The authors cautioned that an unpolarized basis set would fail to pick up these small effects, which they attribute to Coulomb and dispersion components of the interaction. 

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