Projected-Dipole Model for Quantum Plasmonics

TL;DR

This paper introduces a new effective model for quantum plasmonics that combines classical electrodynamics with a quantum-informed dipole layer, enabling accurate simulations of larger nanostructures.

Contribution

The projected-dipole model provides a computationally efficient way to incorporate quantum effects into classical plasmonic simulations, validated against TDDFT data.

Findings

Quantum corrections are significant in sub-nanometric gaps.

The model accurately reproduces TDDFT results for nonlocal response.

Applicable to large systems beyond ab-initio computational limits.

Abstract

Quantum effects of plasmonic phenomena have been explored through ab-initio studies, but only for exceedingly small metallic nanostructures, leaving most experimentally relevant structures too large to handle. We propose instead an effective description with the computationally appealing features of classical electrodynamics, while quantum properties are described accurately through an infinitely thin layer of dipoles oriented normally to the metal surface. The nonlocal polarizability of the dipole layer is mapped from the free-electron distribution near the metal surface as obtained with 1D quantum calculations, such as time-dependent density-functional theory (TDDFT), and is determined once and for all. The model can be applied to any system size that is tractable within classical electrodynamics, while capturing quantum plasmonic aspects of nonlocal response and a finite work function with TDDFT-level accuracy. Applying the theory to dimers we find quantum-corrections to the hybridization even in mesoscopic dimers as long as the gap is sub-nanometric itself.