Quantum description of the plasmon resonances of a nanoparticle dimer.

Using time-dependent density functional theory, we present a fully quantum mechanical investigation of the plasmon resonances in a nanoparticle dimer as a function of interparticle separation. We show that for dimer separations below 1 nm quantum mechanical effects, such as electron tunneling across the dimer junction and screening, significantly modify the optical response and drastically reduce the electromagnetic field enhancements relative to classical predictions. For larger separations, the dimer plasmons are well described by classical electromagnetic theory.