Comment on "Exploring nature and predicting strength of hydrogen bonds: A correlation analysis between atoms-in-molecules descriptors, binding energies, and energy components of symmetry-adapted perturbation theory"

Abstract

We evaluate the correlation between binding energy (BE) and electron density ρ(r) at the bond critical point for 28 neutral hydrogen bonds, recently reported by Emamian and co-workers (J. Comput. Chem., 2019, 40, 2868). As an efficient tool, we use local stretching force constant $k_{\mathrm{HB}}^a$ derived from the local vibrational mode theory of Konkoli and Cremer. We compare the physical nature of BE versus $k_{\mathrm{HB}}^a$ , and provide an important explanation for cases with significant deviation in the BE- $k_{\mathrm{HB}}^a$ relation as well as in the BE-ρ(r) correlation. We also show that care has to be taken when different hydrogen bond strength measures are compared. The BE is a cumulative hydrogen bond strength measure while $k_{\mathrm{HB}}^a$ is a local measure of hydrogen bond strength covering different aspects of bonding. A simplified and unified description of hydrogen bonding is not always possible and needs an in-depth understanding of the systems involved.

Keywords: binding energy; electron density; hydrogen bond; local hydrogen bond energy; local vibrational mode theory.