COLLECTIVE RESONANCES IN SILVER CLUSTERS - ROLE OF D ELECTRONS AND THE POLARIZATION-FREE SURFACE-LAYER

Silver microclusters display giant dipole collective resonances with an unusual size dependence of the resonance frequency. This behavior is due to the fact that the clusters contain polarizable atomic-core d electrons in addition to a delocalized electron cloud. We describe a self-consistent field analysis of the response properties of such a system. It is shown that the efficiency of core screening is controlled by the overlap between d-electron and delocalized-electron wave functions. This provides microscopic justification for the two-region model in which core dielectric screening is missing in a layer near the particle surface. The dipole-excitation energies of such particles are calculated, and it is demonstrated that the model can account for the unusual blueshift of AgN+ resonances. The discussion of the polarization-free layer is also applicable to metallic surfaces. © 1995 The American Physical Society.