Robust Subnanometric Plasmon Ruler by Rescaling of the Nonlocal Optical Response

We present the optical response of two interacting metallic nanowires calculated for separationdistances down to angstrom range. State-of-the-art local and nonlocal approaches are compared withfull quantum time-dependent density functional theory calculations that give an exact account of nonlocaland tunneling effects. We find that the quantum results are equivalent to those from classical approacheswhen the nanoparticle separation is defined as the separation between centroids of the screening charges.This establishes a universal plasmon ruler for subnanometric distances. Such a ruler not only impacts thebasis of many applications of plasmonics, but also provides a robust rule for subnanometric metrology