Electronic structure contribution to hydrogen bonding interaction of a water dimer

TL;DR

This study quantifies the specific molecular orbital contributions to hydrogen bonding in a water dimer, revealing significant covalent-like character and advancing understanding of intermolecular interactions.

Contribution

Introduces an orbital-resolved electron density approach to quantify MO contributions to hydrogen bonds in water dimers, providing new insights into covalent character.

Findings

HOMO-4 accounts for about 40% of electron density at the bond critical point

Orbital interactions lead to electron accumulation, indicating covalent-like H-bond character

Method offers quantitative electronic structure insights into intermolecular systems

Abstract

Hydrogen bond (H-bond) covalency has recently been observed in ice and liquid water, while the penetrating molecular orbitals (MOs) in the H-bond region of most typical water dimer system, (H2O)2, have also been discovered. However, obtaining the quantitative contribution of these MOs to the H-bond interaction is still problematic. In this work, we introduced the orbital-resolved electron density projected integral (EDPI) along the H-bond to approach this problem. The calculations show that, surprisingly, the electronic occupied orbital (HOMO-4) of (H2O)2 accounts for about 40% of the electron density at the bond critical point. Moreover, the charge transfer analysis visualizes the electron accumulating effect of the orbital interaction within the H-bond between water molecules, supporting its covalent-like character. Our work expands the classical understanding of H-bond with specific contributions from certain MOs, and will also advance further research into such covalency and offer quantitative electronic structure insights into intermolecular systems.