Optical
Properties of Silver Nanoshells from Time-Dependent Density Functional
Theory Calculations
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Abstract
The absorption spectra of Ag monatomic
nanoshells of size between 12 and 272 atoms with different shapes
(icosahedra, cuboctahedra, and truncated octahedra) are theoretically
studied via a time-dependent density functional theory approach and
compared with previous results on compact nanoparticles of similar
size and shape. Three main findings are drawn from this study: (a)
Ag monatomic nanoshells possess absorption spectra exhibiting clear
plasmonic features starting already with the 92-atom system; (b) the
position of the absorption peaks moves toward lower energy as the
radius of the nanoshells increases, with a blue shift of β0.2
eV for icosahedral with respect to cuboctahedral shells (also, the
peak substantially gains in intensity with increasing size); (c) the
absorption maxima are strongly red-shifted by 0.8β1.0 eV with
respect to homologous compact arrangements. The red-shift phenomenon (c) is shown
to be due not to a combination mode of internal and external surface
plasmon resonances, as in thicker nanoshells, but rather to the relief
of the charge compression by the underlying metallic layers on the
resonating electrons. An analysis of the character of the electronic
transitions mostly contributing to the absorption peaks finally provides
information on the atomistic character of the corresponding modes