Quantifying the hydration structure of sodium and potassium ions: taking additional steps on Jacob's Ladder

Timothy T. Duignan; Gregory K. Schenter; John L. Fulton; Thomas Huthwelker; Mahalingam Balasubramanian; Mirza Galib; Marcel D. Baer; Jan Wilhelm; Jürg Hutter; Mauro Del Ben; X. S. Zhao; Christopher J. Mundy

doi:10.1039/C9CP06161D

Quantifying the hydration structure of sodium and potassium ions: taking additional steps on Jacob's Ladder

Timothy T. Duignan,

*^ab Gregory K. Schenter,

^a John L. Fulton,^a Thomas Huthwelker,^c Mahalingam Balasubramanian,^d Mirza Galib,

^a Marcel D. Baer,

^a Jan Wilhelm,^ef Jürg Hutter,^e Mauro Del Ben,^g X. S. Zhao

*^b and Christopher J. Mundy

*^ah

Author affiliations

* Corresponding authors

^a Physical Science Division, Pacific Northwest National Laboratory, P. O. Box 999, Richland, Washington 99352, USA
E-mail: chris.mundy@pnnl.gov

^b School of Chemical Engineering, The University of Queensland, St Lucia, Brisbane 4072, Australia
E-mail: t.duignan@uq.edu.au, george.zhao@uq.edu.au

^c Swiss Light Source, Paul Scherrer Institut (PSI), 5232 Villigen, Switzerland

^d X-ray Sciences Division, Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, USA

^e Department of Chemistry, University of Zurich, CH-8057 Zürich, Switzerland

^f Institute of Theoretical Physics, University of Regensburg, D-93053 Regensburg, Germany

^g Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^h Department of Chemical Engineering, University of Washington, Seattle, Washington, USA

Abstract

The ability to reproduce the experimental structure of water around the sodium and potassium ions is a key test of the quality of interaction potentials due to the central importance of these ions in a wide range of important phenomena. Here, we simulate the Na⁺ and K⁺ ions in bulk water using three density functional theory functionals: (1) the generalized gradient approximation (GGA) based dispersion corrected revised Perdew, Burke, and Ernzerhof functional (revPBE-D3) (2) the recently developed strongly constrained and appropriately normed (SCAN) functional (3) the random phase approximation (RPA) functional for potassium. We compare with experimental X-ray diffraction (XRD) and X-ray absorption fine structure (EXAFS) measurements to demonstrate that SCAN accurately reproduces key structural details of the hydration structure around the sodium and potassium cations, whereas revPBE-D3 fails to do so. However, we show that SCAN provides a worse description of pure water in comparison with revPBE-D3. RPA also shows an improvement for K⁺, but slow convergence prevents rigorous comparison. Finally, we analyse cluster energetics to show SCAN and RPA have smaller fluctuations of the mean error of ion–water cluster binding energies compared with revPBE-D3.

This article is part of the themed collection: Frontiers in Molecular Simulation of Solvated Ions, Molecules and Interfaces

Physical Chemistry Chemical Physics

Quantifying the hydration structure of sodium and potassium ions: taking additional steps on Jacob's Ladder

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Quantifying the hydration structure of sodium and potassium ions: taking additional steps on Jacob's Ladder

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