Electron density topography, NMR, and NBO analysis of water clusters

Abstract

Hydrogen bonds (H‐bonds) present in water clusters (H₂O)_n=2-20 are characterized in terms of the electron density (ρ(r_c)) and the Laplacian of the electron density (∇²ρ(r_c)) at the H‐bond critical points (HBCPs) using the atoms‐in‐molecules approach. It is shown that the stabilization energy (SE) of the clusters increases linearly with increase in the value of the sum of the ρ(r_c) values as well as the sum of the ∇²ρ(r_c) values at the HBCPs. Using the geometric and electron density topography criteria, a new parameter that measures the H‐bond strength in multiple H‐bonded systems is proposed. Nuclear magnetic resonance shielding constants for proton (¹H) and oxygen (¹⁷O) have been computed to analyze OH…O interactions for all the water clusters. The charge transfer interaction in the formation of H‐bonds in various water clusters has been assessed with the help of natural bond orbital analysis.