Supporting Information For Electrode Paper

This repo includes code that accompanies the paper "Chapman and Bresme, Electrotunable Kapitza Resistance at Electrode-Water Interfaces: The Importance of Electrode Metallicity" DOI: 10.26434/chemrxiv-2025-qmb0d

Modifications to LAMMPS

This repository includes two patch files, that apply changes to LAMMPS that enabled the use of dynamic electrodes with the finite field method. They apply to different versions of LAMMPS.

The file electrode-patch-old.patch has been tested on December 22 and Aug 23 releases of LAMMPS as well as a development version from June 23 (GITREF). The patch can be applied directly to versions up to git ref (5a455c) from the LAMMPS development branch, though only validated on the aforementioned versions.

The file electrode-patch-new.patch has the same content, but can be applied directly to newer versions of LAMMPS. It has been tested to work with the latest September 2025 release.

The version of the source code used for the water and 1 molal NaCl simulations in our paper can be found in our fork. The 3 molal NaCl simulations used the electrode-patch-old.patch applied to the August 2023 Stable release of LAMMPS.

We endeavour to contribute these changes back upstream as soon as possible.

Applying the patch

After cloning the LAMMPS source code, download the appropriate patch file.

Within the LAMMPS directory simply run,

git apply electrode-patch-new.patch

Changes Made

This patch implements the Finite Field (FF) variant of the Constant Potential Method by Dufils et. al. in conjuction to the conjugate gradient and conjugate gradient matrix solvers. Both the solvers and the FF method were implemented separately before, but did not work together. No was error raised, instead the electrodes had the incorrect potentials.

The patch also fixes a small issue with the etypes option to the fix electrode/conp command. If the option was used with systems that had atom types, but no atoms of that type in the system, the simulation would crash.