  The electronic structure and optical properties of metallic nanoshells are
investigated using a jellium model and the Time Dependent Local Density
Approximation (TDLDA). An efficient numerical implementation enables
applications to nanoshells of realistic size with up to a million electrons. We
demonstrate how a frequency dependent background polarizability of the jellium
shell can be included in the TDLDA formalism. The energies of the plasmon
resonances are calculated for nanoshells of different sizes and with different
dielectric cores, dielectric embedding media, and dielectric shell backgrounds.
The plasmon energies are found to be in good agreement with the results from
classical Mie scattering theory using a Drude dielectric function. A comparison
with experimental data shows excellent agreement between theory and the
measured frequency dependent absorption spectra.
