The Electrodynamical Nature of Chiral Nanoplasmonics from the Quantum Regime to the Mesoscale

Chiral plasmonic nanostructures are rapidly emerging as ideal substrates for enantioselective sensing, chiral near-field engineering, and plasmon-assisted catalysis, owing to their exceptional sensitivity to structural handedness. However, whether an atomistic classical electrodynamic description can capture the plasmonic chiroptical response across size regimes spanning from the quantum to the mesoscale remains an open question, limiting the development of predictive theoretical methods for the design of novel chiral plasmonic architectures. Here, we show that a fully atomistic classical electrodynamic model, coupling intraband charge transport and interband polarization, quantitatively reproduces state-of-the-art ab initio and experimental chiroptical spectra across the quantum-to-classical regime, from atomistically defined chiral Ag and Au nanostructures to DNA-origami-assembled Au nanorods containing up to ∼105 atoms. Our results show that a classical atomistic description remains valid in both the quantum regime and the mesoscale, providing the missing foundation to connect local structural motifs to chiroptical response and paving the way for the atomistically defined, rational design of chiral plasmonic nanostructures optimized for targeted applications.