Density functional study of structural and electronic properties of bimetallic silver–gold clusters: Comparison with pure gold and silver clusters

Bonacˇic´-Koutecky´, Vlasta; Burda, Jaroslav; Mitric´, Roland; Ge, Maofa; Zampella, Giuseppe; Fantucci, Piercarlo
August 2002
Journal of Chemical Physics;8/15/2002, Vol. 117 Issue 7, p3120
Academic Journal
Bimetallic silver-gold clusters offer an excellent opportunity to study changes in metallic versus "ionic" properties involving charge transfer as a function of the size and the composition, particularly when compared to pure silver and gold clusters. We have determined structures, ionization potentials, and vertical detachment energies for neutral and charged bimetallic Ag[sub m]Au[sub n][3 ≤ (m+n) ≤5] clusters. Calculated VDE values compare well with available experimental data. In the stable structures of these clusters Au atoms assume positions which favor the charge transfer from Ag atoms. Heteronuclear bonding is usually preferred to homonuclear bonding in clusters with equal numbers of hetero atoms. In fact, stable structures of neutral Ag[sub 2]Au[sub 2], Ag[sub 3]Au[sub 3], and Ag[sub 4]Au[sub 4] clusters are characterized by the maximum number of hetero bonds and peripheral positions of Au atoms. Bimetallic tetramer as well as hexamer are planar and have common structural properties with corresponding one-component systems, while Ag[sub 4]Au[sub 4] and Ag[sub 8] have 3D forms in contrast to Au[sub 8] which assumes planar structure. At the density functional level of theory we have shown that this is due to participation of d electrons in bonding of pure Au[sub n] clusters while s electrons dominate bonding in pure Ag[sub m] as well as in bimetallic clusters. In fact, Au[sub n] clusters remain planar for larger sizes than Ag[sub m] and Ag[sub n]Au[sub n] clusters. Segregation between two components in bimetallic systems is not favorable, as shown in the example of Ag[sub 5]Au[sub 5] cluster. We have found that the structures of bimetallic clusters with 20 atoms Ag[sub 10]Au[sub 10] and Ag[sub 12]Au[sub 8] are characterized by negatively charged Au subunits embedded in Ag environment. In the latter case, the shape of Au[sub 8] is related to a pentagonal bipyramid capped by one atom and contains three exposed negatively charged Au atoms. They might...


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