Why Dissolving Salt in Water Decreases Its Dielectric Permittivity

Chunyi Zhang, Shuwen Yue, Athanassios Z. Panagiotopoulos, Michael L. Klein, and Xifan Wu

Phys. Rev. Lett. 131, 076801 – Published 16 August 2023

Abstract

The dielectric permittivity of salt water decreases on dissolving more salt. For nearly a century, this phenomenon has been explained by invoking saturation in the dielectric response of the solvent water molecules. Herein, we employ an advanced deep neural network (DNN), built using data from density functional theory, to study the dielectric permittivity of sodium chloride solutions. Notably, the decrease in the dielectric permittivity as a function of concentration, computed using the DNN approach, agrees well with experiments. Detailed analysis of the computations reveals that the dominant effect, caused by the intrusion of ionic hydration shells into the solvent hydrogen-bond network, is the disruption of dipolar correlations among water molecules. Accordingly, the observed decrease in the dielectric permittivity is mostly due to increasing suppression of the collective response of solvent waters.

Received 26 January 2023
Revised 30 April 2023
Accepted 7 July 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.076801

Physics Subject Headings (PhySH)

Dielectric properties Electric polarization Permittivity

Water

Density functional theory First-principles calculations Machine learning

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Chunyi Zhang ¹, Shuwen Yue ², Athanassios Z. Panagiotopoulos ², Michael L. Klein ^1,3,4,*, and Xifan Wu ^1,3,†

¹Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA
²Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA
³Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania 19122, USA
⁴Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA