Atomic partial charges in condensed phase from an exact sum rule for infrared absorption

Abstract

A general sum rule for infrared intensities provides a definition of effective partial charges which can be experimentally obtained using isotopic substitutions and is valid in both gas and condensed phases. Of particular interest is the case of molecular liquids. We have, therefore, determined the hydrogen partial charges in liquid methanol and liquid water from the available literature. The resulting charges are 0.63 e and 0.14 e for hydrogen atoms bounded to the methanol oxygen and carbon atoms, respectively, and 0.55 e for hydrogen atoms in liquid water. The effective partial charges in liquid water were also computed from density functional based ab initio molecular dynamics simulations and found in good agreement with experiment.

Keywords:

• atomic polar tensors
• infrared spectroscopy
• sum rule

Acknowledgements

It is a great pleasure to dedicate this paper to Pierre Turq on the occasion of his 70th birthday. The author would also like to thank B. Guillot, D. Borgis, M.-P. Gaigeot, M. Sprik, and P. Madden for very interesting and fruitful discussions.

Additional information

Funding

This work was performed using HPC resources from GENCI-IDRIS (grant number 2013-x2013082309].