Plasmon oscillations in ellipsoid nanoparticles: beyond dipole   approximation
  The plasmon oscillations of a metallic triaxial ellipsoid nanoparticle have been studied within the framework of the quasistatic approximation. A general method has been proposed for finding the analytical expressions describing the potential and frequencies of the plasmon oscillations of an arbitrary multipolarity order. The analytical expressions have been derived for an electric potential and plasmon oscillation frequencies of the first 24 modes. Other higher orders plasmon modes are investigated numerically. 
D.V. Guzatov, V.V. Klimov, M.Yu. Pikhota