4 research outputs found
Photoabsorption of Icosahedral Noble Metal Clusters: An Efficient TDDFT Approach to Large-Scale Systems
7noWe apply a recently developed time-dependent density functional theory (TDDFT) algorithm based on the complex dynamical polarizability to calculate the photoabsorption spectrum of the following series of closed-shell icosahedral clusters of increasing size (namely, [M13]5+, [M55]3−, [M147]−, and [M309]3+ with M = Ag, Au), focusing in particular on their plasmonic response. The new method is shown to be computationally very efficient: it simultaneously retains information on the excited-state wave function and provides a detailed analysis of the optical resonances, e.g., by employing the transition contribution map scheme. For silver clusters, a very intense plasmon resonance is found for [Ag55]3−, with strong coupling among low-energy single-particle configurations. At variance, for gold clusters we do not find a single strong plasmonic peak but rather many features of comparable intensity, with partial plasmonic behavior present only for the lowest-energy transitions. Notably, we also find a much greater sensitivity of the optical response of Ag clusters with respect to Au clusters to cluster charge, the exchange-correlation (xc) functional, and the basis set, as demonstrated via a detailed comparison between [Ag55]q and [Au55]q. The results of the TDDFT algorithm obtained with the
complex dynamical polarizability are finally compared with those produced by alternative (real-time evolution or Lanczos) approaches, showing that, upon proper choice of numerical parameters, overall nearly quantitative agreement is achieved among all of the considered approaches, in keeping with their fundamental equivalence.partially_openopenBaseggio, Oscar; De Vetta, Martina; Fronzoni, Giovanna; Stener, Mauro; Sementa, Luca; Fortunelli, Alessandro; Calzolari, ArrigoBaseggio, Oscar; De Vetta, Martina; Fronzoni, Giovanna; Stener, Mauro; Sementa, Luca; Fortunelli, Alessandro; Calzolari, Arrig
Ligand-Enhanced Optical Response of Gold Nanomolecules and Its Fragment Projection Analysis: The Case of Au<sub>30</sub>(SR)<sub>18</sub>
Here
we investigate via first-principles simulations the optical
absorption spectra of three different Au<sub>30</sub>(SR)<sub>18</sub> monolayer-protected clusters (MPC): Au<sub>30</sub>(S<sup>t</sup>Bu)<sub>18</sub>, Au<sub>30</sub>(SPh)<sub>18</sub>, and Au<sub>30</sub>(SPh-<i>p</i>NO<sub>2</sub>)<sub>18</sub>. Au<sub>30</sub>(S<sup>t</sup>Bu)<sub>18</sub> is known in the literature, and its
crystal structure is available. In contrast, Au<sub>30</sub>(SPh)<sub>18</sub> and Au<sub>30</sub>(SPh-<i>p</i>NO<sub>2</sub>)<sub>18</sub> are two species that have been designed by replacing
the <i>tert</i>-butyl organic residues of Au<sub>30</sub>(S<sup>t</sup>Bu)<sub>18</sub> with aromatic ones so as to investigate
the effects of ligand replacement on the optical response of Au nanomolecules.
By analogy to a previously studied Au<sub>23</sub>(SR)<sub>16</sub><sup>–</sup> anionic species, despite distinct differences
in charge and chemical composition, a substantial ligand enhancement
of the absorption intensity in the optical region is also obtained
for the Au<sub>30</sub>(SPh-<i>p</i>NO<sub>2</sub>)<sub>18</sub> MPC. The use of conjugated aromatic ligands with properly
chosen electron-withdrawing substituents and exhibiting steric hindrance
so as to also achieve charge decompression at the surface is therefore
demonstrated as a general approach to enhancing the MPC photoabsorption
intensity in the optical region. Additionally, we here subject the
ligand-enhancement phenomenon to a detailed analysis based on the
fragment projection of electronic excited states and on induced transition
densities, leading to a better understanding of the physical origin
of this phenomenon, thus opening avenues to its more precise control
and exploitation
Crystal Structure and Theoretical Analysis of Green Gold Au<sub>30</sub>(S‑<i>t</i>Bu)<sub>18</sub> Nanomolecules and Their Relation to Au<sub>30</sub>S(S‑<i>t</i>Bu)<sub>18</sub>
We report the complete X-ray crystallographic
structure as determined
through single-crystal X-ray diffraction and a thorough theoretical
analysis of the green gold Au<sub>30</sub>(S-<i>t</i>Bu)<sub>18</sub>. While the structure of Au<sub>30</sub>SÂ(S-<i>t</i>Bu)<sub>18</sub> with 19 sulfur atoms has been reported, the crystal
structure of Au<sub>30</sub>(S-<i>t</i>Bu)<sub>18</sub> without
the μ<sub>3</sub>-sulfur has remained elusive until now, though
matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS)
and electrospray ionization mass spectrometry (ESI-MS) data unequivocally
show its presence in abundance. The Au<sub>30</sub>(S-<i>t</i>Bu)<sub>18</sub> nanomolecule not only is distinct in its crystal
structure but also has unique temperature-dependent optical properties.
Structure determination allows a rigorous comparison and an excellent
agreement with theoretical predictions of structure, stability, and
optical response
Crystal Structure and Theoretical Analysis of Green Gold Au<sub>30</sub>(S‑<i>t</i>Bu)<sub>18</sub> Nanomolecules and Their Relation to Au<sub>30</sub>S(S‑<i>t</i>Bu)<sub>18</sub>
We report the complete X-ray crystallographic
structure as determined
through single-crystal X-ray diffraction and a thorough theoretical
analysis of the green gold Au<sub>30</sub>(S-<i>t</i>Bu)<sub>18</sub>. While the structure of Au<sub>30</sub>SÂ(S-<i>t</i>Bu)<sub>18</sub> with 19 sulfur atoms has been reported, the crystal
structure of Au<sub>30</sub>(S-<i>t</i>Bu)<sub>18</sub> without
the μ<sub>3</sub>-sulfur has remained elusive until now, though
matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS)
and electrospray ionization mass spectrometry (ESI-MS) data unequivocally
show its presence in abundance. The Au<sub>30</sub>(S-<i>t</i>Bu)<sub>18</sub> nanomolecule not only is distinct in its crystal
structure but also has unique temperature-dependent optical properties.
Structure determination allows a rigorous comparison and an excellent
agreement with theoretical predictions of structure, stability, and
optical response