Quantum nature of the hydrogen bond

Hydrogen bonds are weak, generally intermolecular bonds, which hold much of soft matter together as well as the condensed phases of water, network liquids, and many ferroelectric crystals. The small mass of hydrogen means that they are inherently quantum mechanical in nature, and effects such as zer...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2011-04, Vol.108 (16), p.6369-6373
Main Authors: Li, Xin-Zheng, Walker, Brent, Michaelides, Angelos
Format: Article
Language:English
Subjects:
Bending
Correlation analysis
Covalent bonds
Crystals
Dimers
Ferroelectrics
Hydrogen
hydrogen bonding
Hydrogen bonds
Ice
Liquids
Molecular dynamics
Molecules
Physical Sciences
prediction
Protons
Quantum physics
Studies
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Summary:Hydrogen bonds are weak, generally intermolecular bonds, which hold much of soft matter together as well as the condensed phases of water, network liquids, and many ferroelectric crystals. The small mass of hydrogen means that they are inherently quantum mechanical in nature, and effects such as zero-point motion and tunneling must be considered, though all too often these effects are not considered. As a prominent example, a clear picture for the impact of quantum nuclear effects on the strength of hydrogen bonds and consequently the structure of hydrogen bonded systems is still absent. Here, we report ab initio path integral molecular dynamics studies on the quantum nature of the hydrogen bond. Through a systematic examination of a wide range of hydrogen bonded systems we show that quantum nuclear effects weaken weak hydrogen bonds but strengthen relatively strong ones. This simple correlation arises from a competition between anharmonic intermolecular bond bending and intramolecular bond stretching. A simple rule of thumb is provided that enables predictions to be made for hydrogen bonded materials in general with merely classical knowledge (such as hydrogen bond strength or hydrogen bond length). Our work rationalizes the influence of quantum nuclear effects, which can result in either weakening or strengthening of the hydrogen bonds, and the corresponding structures, across a broad range of hydrogen bonded materials. Furthermore, it highlights the need to allow flexible molecules when anharmonic potentials are used in force field-based studies of quantum nuclear effects.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1016653108