Electronic quantum effect on hydrogen bond geometry in water dimer

TL;DR

This study reveals quantum effects on hydrogen bond and O-H bond lengths in a water dimer under compression, showing how electronic structure influences bond behavior beyond classical predictions.

Contribution

It provides high-precision first-principles analysis of quantum effects on water dimer bonds under compression, highlighting a transition in dominant interactions.

Findings

H-bond length decreases with compression

O-H bond length increases then decreases beyond a stable point

Transition from electrostatic to exchange repulsion interaction

Abstract

During compression of a water dimer calculated with high-precision first-principles methods, the trends of H-bond and O-H bond lengths show quantum effect of the electronic structure. We found that the H-bond length keeps decreasing, while the O-H bond length increases up to the stable point and decreases beyond it when the water dimer is further compressed. The remarkable properties are different from those observed in most previous researches which can be understood and extrapolated through classical simulation. The observations can be explained by the decrease in orbital overlap and change in the exchange repulsion interaction between water monomers. The dominant interaction between water monomers changes from electrostatic interaction to exchange repulsion at the turning point of the O-H bond length when the O...O distance is decreased. These findings highlight the quantum effect on the hydrogen bond in extreme conditions and play an important role in the recognition of the hydrogen bond structure and mechanism.