Interference effects between ion induced solvent polarisations in Liquid water

TL;DR

This study investigates how ion-induced solvent polarization interference affects the effective force between ions in water, revealing deviations from classical models at short distances due to polarization effects.

Contribution

The paper introduces a detailed simulation analysis of ion interactions in water, highlighting polarization interference effects that alter the effective force law at nanometer scales.

Findings

Effective force deviates from classical Coulomb law at <1 nm

Asymmetry observed between positive and negative ions

Distance-dependent dielectric constants exhibit unique features

Abstract

We calculate the effective force between two oppositely charged and similarly charged ions fixed in water as a function of separation distance R. At short separations, R less than 1 nm, the effective force is vastly different from the $1/{\epsilon}_{s}R^2$ dependence advocated by the screened Coulomb force law (SCFL); ${\epsilon}_{s}$ being the static dielectric constant of the medium. We also find an interesting asymmetry in the force between +ve and -ve ions. This breakdown of SCFL is shown to be due to the persistent interference between the polarizations created by the two charges, in a manner similar to the vortex-antivortex pair formation in XY model Hamiltonian. The distance dependence of dielectric constants, ${\epsilon}_{s}$(R) extracted from our simulation exhibit interesting features and can be used in future modelling.