The optical properties of gold semi shell nanopartilces with different shell thicknesses, physical parameters and inter particle separations are theoretically studied by discrete dipole approximation method. The numerical results show that the extinction resonance wavelength of semi shell nanoparticle is first blue shifted and then red shifted as the shell thickness increases, the shell thickness corresponding to resonance wavelength shifting to opposite direction increases with the increase of the dielectric constants of inner core material and embedding medium and with that of the inter particle separation between two semi shell nanoparticles. The shift of the resonance wavelength is ascribed to the mutual interactions between plasmon hybridization and phase retardation. The plasmon hybridization plays an important role as the shell thickness is thin, as the shell thickness gets thicker, phase retardation effect will become significant.
