XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Unraveling nanoparticle properties using density functional theory
Christine M. Aikens
Kansas State University, Manhattan, KS 66506, USA
Theoretical investigations of monolayer-protected noble metal nanoparticles play an important role in determining the origins of the unique chemical and physical properties of these systems that lead to applications in photonics, sensing, catalysis, etc. In contrast to the strong plasmon resonance peak of larger nanoparticles, the optical absorption spectra of small (< 2 nm) nanoparticles display multiple peaks. Time-dependent density functional theory (TDDFT) is employed to examine the spectrum of the Au25(SR)18- nanoparticle, and it is determined that delocalized orbitals in the 13-atom nanoparticle core are primarily responsible for the excited state transitions. The ligand field arising from the surrounding gold-thiolate oligomers is responsible for the splitting of the intraband transition.
In the past decade, several gold and silver nanoparticles have been determined to be chiral. Density functional theory calculations on the Au11(BINAP)4Cl2+ system provide important information regarding ligand effects on core structure and the resulting circular dichroism spectra. The low energy peaks of Au11L4X2+ arise mainly from transitions between delocalized metal superatom orbitals. Bidentate phosphine ligands have both a structural and electronic effect on the system. Whereas monodentate phosphine ligands lead to a C1 geometry, the lowest energy structure of Au11L4X2+ has a chiral C2 structure. The chiral core of Au11L4X2+ is not sufficient to explain the strong Cotton effects, and the intensity of the CD spectrum is increased by the presence of the bidentate phosphine ligands.
Using a combination of electronic structure calculations, XRD, and optical and chiroptical spectra, the “magic” Au38(SR)24 nanocluster is shown to be chiral with D3 symmetry. Au38(SR)24 is found to have an elongated, prolate structure; the electronic structure of this prolate “nanorod” is similar to that previously determined for silver nanorods. As for Au25(SR)18, delocalized superatom-like orbitals are responsible for its properties.


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