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Quadrupole-mediated dielectric response and the charge-asymmetric solvation of ions in water.

Published version
Peer-reviewed

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Authors

Cox, Stephen J 
Mandadapu, Kranthi K 
Geissler, Phillip L 

Abstract

Treating water as a linearly responding dielectric continuum on molecular length scales allows very simple estimates of the solvation structure and thermodynamics for charged and polar solutes. While this approach can successfully account for basic length and energy scales of ion solvation, computer simulations indicate not only its quantitative inaccuracies but also its inability to capture some basic and important aspects of microscopic polarization response. Here, we consider one such shortcoming, a failure to distinguish the solvation thermodynamics of cations from that of otherwise-identical anions, and we pursue a simple, physically inspired modification of the dielectric continuum model to address it. The adaptation is motivated by analyzing the orientational response of an isolated water molecule whose dipole is rigidly constrained. Its free energy suggests a Hamiltonian for dipole fluctuations that accounts implicitly for the influence of higher-order multipole moments while respecting constraints of molecular geometry. We propose a field theory with the suggested form, whose nonlinear response breaks the charge symmetry of ion solvation. An approximate variational solution of this theory, with a single adjustable parameter, yields solvation free energies that agree closely with simulation results over a considerable range of solute size and charge.

Description

Keywords

cond-mat.stat-mech, cond-mat.stat-mech

Journal Title

J Chem Phys

Conference Name

Journal ISSN

0021-9606
1089-7690

Volume Title

154

Publisher

AIP Publishing

Rights

All rights reserved
Sponsorship
U.S. Department of Energy, Award/Contract Number DE-AC02-05CH11231 Royal Commission for the Exhibition of 1851
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