Global Potential Energy Minima of (H$_{2}$O)$_{n}$ Clusters on Graphite

TL;DR

This study identifies the most stable configurations of water clusters on graphite surfaces using basin-hopping optimization and detailed potential models, revealing structural similarities and differences with free water clusters.

Contribution

First comprehensive computational analysis of (H₂O)ₙ clusters on graphite surfaces using advanced potential models and basin-hopping optimization.

Findings

Global minima often resemble free water clusters.

Water-graphite interaction is predominantly hydrophobic.

Structural subunits are conserved in many cases.

Abstract

Likely candidates for the global potential energy minima of (H$_{2}$O)$_{n}$ clusters with $n\leq21$ on the (0001)-surface of graphite are found using basin-hopping global optimization. The potential energy surfaces are constructed using the TIP4P intermolecular potentials for the water molecules (the TIP3P is also explored as a secondary choice), a Lennard-Jones water-graphite potential, and a water-graphite polarization potential that is built from classical electrostatic image methods and takes into account both the perpendicular and parallel electric polarizations of graphite. This potential energy surface produces a rather hydrophobic water-graphite interaction. As a consequence, the water component of the lowest graphite-(H$_{2}$O)$_{n}$ minima is quite closely related to low-lying minima of the corresponding TIP4P (H$_{2}$O)$_{n}$ clusters. In about half of the cases the geometrical substructure of the water molecules in the graphite-(H$_{2}$O)$_{n}$ global minimum coincides with that of the corresponding free water cluster. Exceptions occur when the interaction with graphite induces a change in geometry. A comparison of our results with available theoretical and experimental data is performed.