Introduction of quantum finite-size effects in the Mie's theory for a multilayered metal sphere in the dipolar approximation: Application to free and matrix-embedded noble metal clusters

A mixed classical/quantum model for calculating the optical response of free and matrix-embedded multilayered metal spheres in the dipolar approximation is presented. The conduction electrons are quantum-mechanically treated in the framework of the time-dependent local-density-approximation formalism (TDLDA), whereas the surrounding matrix, the ionic metal backgrounds and the non-metallic materials are classically described through homogeneous charge distributions or/and dielectric media. Except for the TDLDA calculations, the present formalism is completely analytical and can be applied to coated spheres with any number of metal or dielectric layers. Contrary to the previous TDLDA-based models involving an inner or/and an outer dielectric medium (one or two interfaces), all the dielectric effects (screening and absorption) are self-consistently calculated. In particular, the interband transitions and the mutual interplay between the conduction and core electrons are self-consistently treated. The deficiencies of the previous models are analyzed, and the results are compared with the classical Mie's theory, over the entire spectral range. The building-up of the classical absorption spectrum, consisting of the surface plasmon resonance and the interband transitions, is clearly observed as the cluster size increases. Received 15 March 1999 and Received in final form 11 October 1999