A systematic search for minimum structures of small gold clusters Aun (n=2–20) and their electronic properties

Abstract

A systematic search for global and energetically low-lying minimum structures of neutral gold clusters Au(n) (n=2-20) is performed within a seeded genetic algorithm technique using density functional theory together with a relativistic pseudopotential. Choosing the energetically lowest lying structures we obtain electronic properties by applying a larger basis set within an energy-consistent relativistic small-core pseudopotential approach. The possibility of extrapolating these properties to the bulk limit for such small cluster sizes is discussed. In contrast to previous calculations on cesium clusters [B. Assadollahzadeh et al., Phys. Rev. B 78, 245423 (2008)] we find a rather slow convergence of any of the properties toward the bulk limit. As a result, we cannot predict the onset of metallic character with increasing cluster size, and much larger clusters need to be considered to obtain any useful information about the bulk limit. Our calculated properties show a large odd-even cluster size oscillation in agreement, for example, with experimental ionization potentials and electron affinities. For the calculated polarizabilities we find a clear transition to lower values at Au14, the first cluster size where the predicted global minimum clearly shows a compact three-dimensional (3D) structure. Hence, the measurement of cluster polarizabilities is ideal to identify the 2D-->3D transition at low temperatures for gold. Our genetic algorithm confirms the pyramidal structure for Au20.

Far-IR Spectra of Small Neutral Gold Clusters in the Gas Phase

“…There have been many theoretical studies addressing this topic. For the neutrals, the small sizes are found to be planar [12][13][14][15][16][17][18][19]. In contrast to what can be inferred from the studies on the ions, there have been some predictions that the dimensionality change for the neutrals may occur at or even below Au8 [20][21][22].…”

“…For comparison with the experimental spectra, IR spectra are calculated for the various low-energy isomers of the pure Aun clusters that have been suggested in the literature [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Computations are performed within TURBOMOLE V6.4 [46] using density functional theory employing the def2-TZVP basis set (with the associated effective core potential def2-ecp) [47] and the Tao-PerdewStaroverov-Scuseria meta-GGA functional [48].…”

Application of a parallel genetic algorithm to the global optimization of medium-sized Au–Pd sub-nanometre clusters

“…The exact 2D-3D transition point for neutral Au clusters is disputed theoretically and experimental evidence is scarce. Theoretical predictions of the 2D-3D crossover point have previously ranged from N = 7-14 atoms [54][55][56][57]. This range is consistence with the evolution of structure-symmetry for Au clusters reported here.…”

A first principles density functional investigation of ligand-protected eight atom gold nanoclusters

“…Theoretical calculations for neutral clusters have predicted the transition to occur at six, 8 seven, 9, 10 eight 11,12 as well as in the range from 11-15 atom clusters. [13][14][15][16][17][18][19][20] It has been anticipated that the different methods and models adopted to determine the cluster size at which the 2D-3D transition takes place can possibly be one of the reasons for the large spread in the obtained results (from [6][7][8][9][10][11][12][13][14][15]. Gold clusters are reported to retain their planar structures to cluster sizes larger compared to Ag and Cu clusters which remain planar upto 7 atom cluster sizes only.…”

“…Several experimental and theoretical studies have predicted this number to fall in a range from 6 to 13. [8][9][10][11][12][13][14][15][16][17][18][19][20] For anionic and cationic gold clusters the 2D-3D transitions are observed to occur at N = 13 and N = 8, respectively. Theoretical calculations for neutral clusters have predicted the transition to occur at six, 8 seven, 9, 10 eight 11,12 as well as in the range from 11-15 atom clusters.…”