Quantum chemical methods are used to assess the importance of a number of factors contributing to H bond strength. The electrostatic component appears to reproduce fairly well the energetic cost of bending an H bond, either an ionic one such as (H2OH⋯OH2)+ or a neutral pair as in HOH⋯OH2. Expansion of the full Coulombic interaction into its multipole series yields insights into the underlying cause of these distortion energies, in addition to the fundamentally different clustering behavior of K+ and the nearly spherical NH+4. The correction to the electrostatic term that arises at the correlated level appears to be at least as important as dispersion, and to be considerably more anisotropic.
- hydrogen bonds