Orientational Interpolation of the Optical Spectra of Nonspherical Nanoparticles

A general method called orientational interpolation (OI) is introduced to compute arbitrary-orientation and orientation averaged optical spectra of nonspherical plasmonic nanoparticles starting from a small number (4-7) of simulated spectra at fixed orientations. OI is a postprocessing method independent of the choice of simulation technique. It uses scattered data approximation on the configuration manifold of the particle and exploits electrodynamic and point-group symmetries to make efficient use of simulation results. OI is shown to agree closely with the exact solution for a silver ellipsoid in the dipole limit and with the more complicated orientation dependence of a larger ellipsoid. The method is then applied successfully to describe the ensemble UV visible spectra of colloidal silver decahedra and pentatwinned nanorods. OI provides insight into the orientation-dependent plasmon lineshapes of nonspherical nanoparticles and will be of practical use as the computational counterpart of the spectroscopy of single particles and randomly oriented ensembles.