OPTICAL-PROPERTIES OF GOLD METAL-CLUSTERS - A TIME-DEPENDENT LOCAL-DENSITY-APPROXIMATION INVESTIGATION

The optical response of free and matrix-embedded gold metal clusters A u-N is investigated in the framework of the time-dependent local-densi ty-approximation (TDLDA). The characteristics of the surface plasmon r esonance are carefully analysed as a function of the model parameters and the particle radius. The strong influence of the frequency-depende nce of the 5d core-electron dielectric function in the vicinity of the interband threshold is emphasized. The size evolution of the Mie-freq uency in free gold clusters exhibits a noticeable blue-shift trend as the particle size decreases, much stronger than in silver clusters. Th e width and shape of the resonance, essentially ruled by the decay via the interband transitions, are found closely correlated to the imagin ary component of the core-electron dielectric function. In presence of a surrounding matrix the blue-shift trend is largely rubbed out. Agre ement with recent experimental results on size-selected gold clusters embedded in an alumina matrix may be achieved by taking into account t he porosity effects at the metal/matrix interface. The comparison with the predictions of classical models is also provided.