First-Principles Investigation of the Atomic and Electronic Structure and Magnetic Moments in Gold Nanoclusters

Abstract

We determine the structure, energetics, and emerging magnetic propertiesof Au n clusters using first-principles plane-wave density functional theory. We compare and contrast the findings obtained with and without spin-orbit interaction in the gold clusters of sizes down to 0.5-1 nm. The shapes are chosen to be representative of spherical gold nanoparticles: (a) Au 13 and Au 12 , with cuboctahedral, icosahedral, and decahedral structures, and (b) Au 25 and Au 24 , with truncated octahedral structures. We find that the trends in the binding energies are unaltered with the choice of the exchange correlation (LDA or GGA) or the inclusion of relativistic effects. The cuboctahedral Au 13 is found to have the lowest binding energy compared with others at a given level of theory. Within the scalar relativistic description, these gold clusters exhibit a wide variety of magnetic moments: the stability and magnetic properties can be readily understood in terms of degeneracies of the HOMO and LUMO levels. Further, there is evidence of Jahn-Teller activity in the cases of cuboctahedral Au 12 and Au 13 that leads to structural distortion, inducing magnetism in the 12-atom cluster. Analysis of electronic states with projection on atomic orbitals for the scalar relativistic case shows that the magnetism in these gold clusters has an sp rather than the otherwise believed s character. By employing a fully relativistic description with inclusion of spin-orbit interaction and noncollinear magnetization, the magnetic moment in the icosahedral-shaped clusters is found to reduce substantially and that in the 12-and 13-atom clusters with a cuboctahedral structure becomes vanishingly small. The loss of magnetism in Au 12 and Au 13 appears to originate from the splitting of degenerate HOMO states in these clusters and an overlap of the d and sp states, whereas the magnetic moment of around 1 μ B in Au 25 is mainly caused by the s states of the central atom.

Protein-protected luminescent noble metal quantum clusters: an emerging trend in atomic cluster nanoscience

“…Representations of naked, phosphine, thiol, and DNA protected clusters were adapted from references (56, 59, 58) and (42), respectively.…”

Chemically Induced Magnetism in Atomically Precise Gold Clusters

“…[ 16 ] The anionic Au 25 [(SC 2 H 4 Ph) 18 ] − clusters were however oxidized to neutral Au 25 (SC 2 H 4 Ph) 18 clusters through aerial oxidation [ 21 ] before the magnetic measurements were carried out on them. The spectrum for Au 38 (SC 12 H 25 ) 24 clusters show step-wise absorption bands at 400 nm and 625 nm respectively, which represent the characteristic bands for the clusters. [ 17 ] The spectrum for Au 55 (PPh 3 ) 12 Cl 6 clusters exhibit no peaks but an approximately exponential decay with increasing wavelength, that matches the spectra reported by Schmid et al [ 22 ] Figure S2 shows the matrix-assisted laser desorption ionization mass spectrum (MALDI-MS, using trans -2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene] malanonitrile (DCTB) as the matrix) for the as-synthesized thiol and mixed-ligand stabilized Au 25 clusters and Au 38 clusters.…”

“…[ 24,25 ] The electronic structure calculations on bulk gold show that the d band lies below the Fermi level where the density of states is too low to stimulate noticeable Pauli paramagnetism. As a result, the weak 5 d band paramagnetism is overcome by a combination of Landau and core diamagnetism giving rise to diamagnetism in bulk gold.…”

Ligand and Solvent Effects on the Structural and Optical Properties of Au13L8 3+ Clusters: a Density Functional Theory Study

“…26 Besides that, this cluster exists in a variety of structures, a fact that is explored in many studies. [27][28][29][30] The most popular one shows icosahedral (I h ) symmetry, since it is present as subunits of larger clusters, like Au 25 31 and Au 38 . 32 On the other hand, the structures of smaller clusters such as Au 9 and Au 11 are observed as fragments of icosahedral Au 13 .…”

“…27,33 Nonetheless, other Au 13 isomers have been studied: cuboctahedron, decahedron, planar and flake. 28,30,34 Ding et al, 34 in a theoretical study, investigated through density functional theory (DFT) calculations the energetic stability of some of these geometrical structures. The results indicate that the planar structure of Au 13 is the most stable in energy.…”