Bias-dependent local structure of water molecule at a metallic interface

TL;DR

This paper presents a combined DFT and NEGF approach to simulate the local structure of water molecules at metallic interfaces under bias, revealing how electric fields influence water orientation and position.

Contribution

It introduces a novel simulation framework that accurately models water-metal interfaces under bias by integrating DFT with NEGF methods, capturing out-of-equilibrium effects.

Findings

Water dipole aligns with electric field

Bias causes asymmetric attraction or repulsion of water

Method enables realistic simulation of electrochemical interfaces

Abstract

Understanding the local structure of water at the interfaces of metallic electrodes is a key problem in aqueous-based electrochemistry. Nevertheless, a realistic simulation of such setup is challenging, particularly when the electrodes are maintained at different potentials. To correctly compute the effect of an external bias potential applied to truly semi-infinite surfaces, we combine Density Functional Theory (DFT) and Non-Equilibrium Green's Functions (NEGF) methods. This framework allows for the out-of-equilibrium calculation of forces and dynamics, and directly correlates to the chemical potential of the electrodes, which is the one introduced experimentally. In this work, we apply this methodology to study the electronic properties and atomic forces of one water molecule at the interface of gold surface. We find that the water molecule tends to align its dipole moment with the electric field, and it is either repelled or attracted to the metal depending on the sign and magnitude of the applied bias, in an asymmetric fashion.