# Lennard–Jones Parameter Fitting for Gold/Water Interaction Based on Structural Analysis: A QM, MM, and QM/MM Study

## TL;DR

This paper proposes a new method for fitting Lennard–Jones parameters for gold/water interactions using structural analysis instead of energy matching.

## Contribution

A novel structural-based approach for fitting LJ parameters for metal/water interactions is introduced and validated.

## Key findings

- Structural analysis of gold/water interactions improves LJ parameters compared to traditional energy-based methods.
- QM/MM simulations confirm that the fitted parameters closely match QM results at lower computational cost.
- The approach can be extended to more complex systems involving water structuring on metallic surfaces.

## Abstract

The interaction between water and metallic interfaces is crucial in many fields, and accurate modeling requires good parametrizations using reference data. In classical molecular dynamics (MD), an important part of this interaction is described using the Lennard–Jones (LJ) potential. However, previously reported LJ parameters are not always optimal for capturing the metal/water interactions observed in ab initio descriptions such as density functional theory (DFT). Therefore, well-tailored LJ parameters are necessary to improve the description of water structuring metals in classical MD. The usual route for obtaining LJ parameters involves energetic analysis, where the energies of various structures are obtained via DFT calculations and then matched with the energies obtained using the LJ potentials by varying the sigma/epsilon parameters. Here, we show a different approach to fit LJ parameters for metal/water interactions, based on structural analysis. We report several classical MD simulations for gold/water, varying the sigma/epsilon parameters, comparing the resulting water structuring with that obtained using DFT. Additionally, we test these parameters in quantum mechanics/molecular mechanics (QM/MM) MD simulations, where electrostatic interactions are enabled. Our results demonstrate that the proposed approach can improve the LJ parameters reported in the literature and potentially develop parameters for more complex systems where the water structure above metallic surfaces plays a significant role. Finally, within this proposed approach, the water density profile obtained in hybrid QM/MM calculations, where water is treated as MM at a substantially reduced cost, closely matches the description it would have if treated as QM.