Ab initio molecular dynamics study of dissociation of water under an electric field

TL;DR

This study uses ab initio molecular dynamics to investigate how water molecules dissociate under electric fields, revealing threshold effects and ionic conductance consistent with experiments, advancing microscopic understanding of electrochemical phenomena.

Contribution

First ab initio molecular dynamics simulation of water under electric fields, showing detailed dissociation mechanisms and conductance at the microscopic level.

Findings

Hydrogen-bond length and orientation are significantly affected by electric fields.

Molecules dissociate and ionic currents are sustained beyond 0.35 V/Å.

At 1.0 V/Å, 15-20% of molecules dissociate, matching experimental conductance.

Abstract

The behavior of liquid water under an electric field is a crucial phenomenon in science and engineering. However, its detailed description at a microscopic level is difficult to achieve experimentally. Here we report on the first ab initio molecular-dynamics study on water under an electric field. We observe that the hydrogen-bond length and the molecular orientation are significantly modified at low-to-moderate field intensities. Fields beyond a threshold of about 0.35 V/\AA are able to dissociate molecules and sustain an ionic current via a series of correlated proton jumps. Upon applying even more intense fields (1.0 V/\AA), a 15-20% fraction of molecules are instantaneously dissociated and the resulting ionic flow yields a conductance of about 7.8 $\Omega^{-1}cm^{-1}$, in good agreement with experimental values. This result paves the way to quantum-accurate microscopic studies of the effect of electric fields on aqueous solutions and, thus, to massive applications of ab initio molecular dynamics in neurobiology, electrochemistry and hydrogen economy.