Water Lone Pair Delocalization in Classical and Quantum Descriptions of the Hydration of Model Ions

Journal Article · Mon Oct 02 04:00:00 EDT 2017 · Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

DOI:https://doi.org/10.1021/acs.jpcb.7b10722· OSTI ID:1439014

Remsing, Richard C. ^[1]; Duignan, Timothy T. ^[2]; Baer, Marcel D. ^[2]; Schenter, Gregory K. ^[2]; Mundy, Christopher J. ^[3]; Weeks, John D. ^[4]

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1. Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania 19122, United States
2. Chemical and Materials Science Division, Pacific Northwest National Laboratory, Richland, Washington, United States
3. Chemical and Materials Science Division, Pacific Northwest National Laboratory, Richland, Washington, United States; Affiliate Professor, Department of Chemical Engineering, University of Washington, Seattle, Washington, United States
4. Institute for Physical Science and Technology and Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States

Understanding the nature of ionic hydration at a fundamental level has eluded scientists despite intense interest for nearly a century. In particular, the microscopic origins of the asymmetry of ion solvation thermodynamics with respect to the sign of the ionic charge remains a mystery. Here, we determine the response of accurate quantum mechanical water models to strong nanoscale solvation forces arising from excluded volumes and ionic electrostatic fields. This is compared to the predictions of two important limiting classes of classical models of water with fixed point changes, differing in their treatment of "lone-pair" electrons. Using the quantum water model as our standard of accuracy, we find that a single fixed classical treatment of lone pair electrons cannot accurately describe solvation of both apolar and cationic solutes, underlining the need for a more flexible description of local electronic effects in solvation processes. However, we explicitly show that all water models studied respond to weak long-ranged electrostatic perturbations in a manner that follows macroscopic dielectric continuum models, as would be expected. We emphasize the importance of these findings in the context of realistic ion models, using density functional theory and empirical models, and discuss the implications of our results for quantitatively accurate reduced descriptions of solvation in dielectric media.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1439014
• Report Number(s): PNNL-SA-130323; KC0301050
• Journal Information: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Journal Name: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry Journal Issue: 13 Vol. 122; ISSN 1520-6106
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English