Au₃₄^-:  A Fluxional Core−Shell Cluster

Abstract

Among the large Au n - clusters for n > 20, the photoelectron spectra of Au34 - exhibit the largest energy gap (0.94 eV) with well-resolved spectral features, making it a good candidate for structural consideration in conjunction with theoretical studies. Extensive structural searches at several levels of density functional and ab initio theory revealed that the low-lying isomers of Au34 - can be characterized as fluxional core−shell type structures with 4 or 3 inner atoms and 30 or 31 outer atoms, i.e., Au4@Au30 - and Au3@Au31 -, respectively. Detailed comparisons between theoretical and photoelectron results suggest that the most probable ground state structures of Au34 - are of the Au4@Au30 - type. The 30 outer atoms seem to be disordered or fluxional, giving rise to a number of low-lying isomers with very close energies and simulated photoelectron spectra. The fluxional nature of the outer layer in large gold clusters or nanoparticles may have important implications for their remarkable catalytic activities.

Fluxionality of gold nanoparticles investigated by Born-Oppenheimer molecular dynamics

“…Photoelectron spectra of Au 34 − display a large energy gap between ground state and higher binding energies [38] consistent with the shell closing of neutral Au 34 cluster [94]. This observation is consistent with a particular stability of this cluster.…”

“…The basin found is represented in Fig. 12 (Cartesian Coordinates available as Auxiliary Material [69]) and is consistent with the minimum energy structures already described for the anion Au 34 − [38,82].…”

“…Nano-sized gold particles have been shown to possess a range of structures lying in a close energy range and to be fluxional at room temperature in the time scale of a few tens of picoseconds. The remarkable property of fluxionality for gold nano-clusters [36,38] is consistent with the structural instability of ultrafine metal particles observed by Iijima and Ichihashi and by Ajayan and Marks [43,44]. In our study fluxionality in the picoseconds regime, corresponding to the timescale of chemical reactivity, has been described for all the investigated systems, and local minima associated with specific numbers of atoms have been isolated and their geometrical and electronic properties have been analyzed and discussed.…”

“…Au 13 has a fluxional structure [35][36][37][38]. Many local minima, very close in energy and interconvertible through low lying energy barriers, coexist at 300 K. The substantially flat energy observed after the first 10 ps (Fig.…”

“…Nonetheless only few contributions are present in the literature concerning the fluxionality of gold particles [35][36][37][38]. In general, a detailed understanding of the relation between structure and properties of gold nanoparticles could lead to the 3 tailoring of electronic properties such as optical, redox and chemical behavior.…”