Multiscale simulation of Raman images of water hexamers in a plasmonic nanocavity

Tip-enhanced Raman imaging can provide insights into the structural and chemical properties of adsorbed systems at the single-molecule scale. In this work, we demonstrate a multiscale method that combines classical electromagnetic simulations and first-principles calculations for the modeling of single-molecule Raman images. The electromagnetic simulation enables the precise description of the near field of the plasmonic nanocavity formed by the tip and substrate as commonly used in the experiments and, thus, allows a realistic calculation of Raman images. This method was applied for the simulation of the non-resonant Raman images for adsorbed water hexamers in two typical configurations, namely, the boat and chair configurations. The simulated Raman images, which reflect the real spatial distribution of the corresponding vibrations, show distinct symmetry differences for the two configurations. The boat configuration features a dumbbell-shaped distribution, while the chair configuration displays triangular symmetry, offering a practical means to identify each structure. Detailed analysis further illuminates the capability to study in real space the hydrogen bonding in the water hexamers, which could be helpful to our understanding of such important interactions at the single-molecule scale.