Electromagnetic response behavior of binary metallic nanoparticles: a comparison of results from a few models of different schematicity

The light absorption of isolated bimetallic alloy nanoparticles composed of Au and Ag is investigated theoretically according to the traditional Mie theory and use of dielectric data. Particular attention is turned to establish the dependence of the absorption on both particle size and composition. The complex dielectric function of clusters involving 254 and 440 active electrons and different stoichiometry has been evaluated on the basis of various models of different degrees of schematicity (Drude theory, noninteracting quantum gas confined in a box, DFT approach), assuming in any case a simple combining rule for the alloy dielectric behavior. The interband contribution to the dielectric function is approximately estimated so as to assess the role of bound-electron effects.