Density functional study on structural and electronic properties of bimetallic gold-yttrium clusters: comparison with pure gold and yttrium clusters

Employing first-principles methods, based on the density functional theory, this paper investigates the ground state geometric and electronic properties of pure gold clusters, pure yttrium clusters and gold clusters doped each with one yttrium atom. It is shown that the average bond lengths in the Aun-1Y(n <= 9) bimetallic clusters are shorter than those in the corresponding pure gold and yttrium clusters. The most stable isomers of the yttrium-doped gold clusters tend to equally delocalize valence s, p and d electrons of the constituent atoms over the entire structure. The Y atom has maximum number of neighbouring Au atom, which tends to be energetically favourable in the lowest-energy equilibrium structures, because the Au Y bond is stronger than the Au-Au bond. The three-dimensional isomers of Aun-1Y structures are found in an early appearance starting at n=5 (Au4Y). Calculated vertical ionization potential and electron affinities as a function of the cluster size show odd-even oscillatory behaviour, and resemble pure gold clusters. However, one of the most striking feature of pure yttrium clusters is the absence of odd-even alternation, in agreement with mass spectrometric observations. The HOMO-LUMO gap of Au3Y is the biggest in all the doped Aun-1Y(n <= 9) bimetallic clusters.