Nonclassical Optical Response of Particle Plasmons With Quantum-Informed Local Optics

As the dimensions of plasmonic structures or the field confinement length approach the mean free path of electrons, mesoscopic optical response effects, including nonlocality, electron spill-in or spill-out, and Landau damping, are expected to become observable. In this work, a quantum-informed local analogue model (QILAM) that maps these nonclassical optical responses onto a local dielectric film is presented. The primary advantage of this model lies in its compatibility with the highly efficient boundary element method (BEM), which includes retardation effects with relatively large particle sizes. Furthermore, the approach offers a unified framework that connects two important semiclassical theories: the generalized nonlocal optical response (GNOR) theory and the Feibelman d-parameters formalism. It is envisioned that QILAM can evolve into a multiscale electrodynamic tool for exploring nonclassical optical responses in diverse plasmonic structures in the future. This can be achieved by directly translating mesoscopic effects into observable phenomena, such as plasmon resonance energy shifts and linewidth broadening in the scattering spectrum.