From discrete electronic states to plasmons:: TDDFT optical absorption properties of Agn (n = 10, 20, 35, 56, 84, 120) tetrahedral clusters

Time-dependent density functional theory calculations are employed to calculate the optical absorption spectra of silver tetrahedral Ag-n (n = 10, 20, 35, 56, 84, 120) clusters with emphasis on neutral and ion clusters that correspond to shell closings. For the Ag-20 cluster, the convergence properties of the spectra with respect to basis set and density functional are examined, and the most accurate results are found to be in good agreement with experimental data. The Ag-n spectra evolve from molecular-like to plasmon-like with increasing n, and from this we are able to extrapolate the plasmon energy and width to the large particle limit, leading to results that are in excellent agreement with continuum electrodynamics results. The results show that for the selected tetrahedral clusters, the plasmon width does not increase with decreasing cluster size as is commonly found (or assumed) for typical cluster shape distributions.