  The description of optical properties of subnanometer junctions is
particularly challenging. Purely classical approaches fail, because the quantum
nature of electrons needs to be considered. Here we report on a novel classical
fully atomistic approach, {\omega}FQ, based on the Drude model for conduction
in metals, classical electrostatics and quantum tunneling. We show that
{\omega}FQ is able to reproduce the plasmonic behavior of complex metal
subnanometer junctions with quantitative fidelity to full ab initio
calculations. Besides the practical potentialities of our approach for large
scale nanoplasmonic simulations, we show that a classical approach, in which
the atomistic discretization of matter is properly accounted for, can
accurately describe the nanoplasmonics phenomena dominated by quantum effects.
