Nanoparticle plasmon resonances in the near-static limit.

Localized surface plasmon resonances of metal nanoparticles of arbitrary shape are analyzed in the near-static limit with retardation included to the second order. Starting from the electrostatic approximation, the second-order correction to the resonant dielectric constant is expressed by means of a triple surface integral. For arbitrary nanoparticles with cylindrical symmetry we show how the triple surface integral can be significantly simplified, resulting in a computationally efficient scheme for evaluation of nanoparticle plasmon eigenresonances in the near-static limit. The approach allows for calculation of both dipolar and higher-order resonances.