Atomistic Nanoplasmonics from Bulk Permittivity

The accurate description of the optical and chiroptical response of plasmonic nanostructures by classical methods requires a physically consistent combination of atomistic treatment with both intraband and interband effects. Here, we show that this can be achieved within a minimal microscopic description based on a single fluctuating charge per atom. In the resulting model, named frequency-dependent fluctuating charges with interband (ωFQ-IB), the charge dynamics is determined by the bulk complex permittivity of the material, which effectively accounts for intraband transport, d-electron screening, and interband transitions, while quantum tunneling across subnanometer gaps is incorporated through a phenomenological function. This minimal representation closely reproduces state-of-the-art ab initio calculations and experimental measurements for a broad range of Ag and Au nanostructures, from few-atom clusters and plasmonic dimers exhibiting quantum tunneling to chiral assemblies and nanoparticles composed of more than one million atoms. By bridging bulk electrodynamics and atomistic description, ωFQ-IB provides a minimal, computationally efficient approach for modeling optical and chiroptical nanoplasmonics of realistic nanostructures.