Resonant surface plasmons of a metal nanosphere can be considered in the   way of propagating surface plasmons
  Assuming that the resonant surface plasmons on a spherical nanoparticle is formed by standing waves of two counter-propagating surface plasmon waves along the surface, by using Mie theory simulation, we find that the dispersions of surface plasmon resonant modes supported by silver nanospheres match that of the surface plasmons on a semi-infinite medium-silver interface very well. This suggests that the resonant surface plasmons of a metal nanosphere can be treated as a propagating surface plasmon wave. 
Yurui Fang and Xiaorui Tian
physics.optics cond-mat.mes-hall