Localized Surface Plasmon Resonance in Free Silver Nanoclusters Ag n , n = 20–147

International audienceAbsorption spectra of silver nanoclusters, Ag n with n = 20−147, are investigated in the framework of the time-dependent density functional theory (TDDFT) with the use of a range-separated hybrid density functional. Our calculated spectra reproduce well the experimental data. The plasmon-like band energy is situated at about 4 eV for all clusters in gas phase. A description of the plasmonic behavior is given using analyses and tools derived from ab initio quantum calculations. The plasmon band originates from multiple peaks gathered in a relatively small range of energy. High intensive peaks near the center of the band present a strong plasmonic character which has been characterized in terms of transition density, hole-electron excitation, transition contribution map (TCM), and generalized plasmonicity index (GPI)