  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.
