Oxidation of Al doped Au clusters: A first principles study.

Using first principles method we report the oxidation of Al doped Au clusters. This work is divided into two parts: (i) the equilibrium structures and stability of Al doped Aun-1 clusters (n=2–7,21) and (ii) the interaction of O2 with stable clusters. The calculations are performed using the plane wave pseudopotential approach under the density functional theory and generalized gradient approximation for the exchange and correlation functional. The optimized geometries of Aun-1Al clusters indicate that the substitution of Au by Al results an early onset of three-dimensional structures from tetramer onwards. This is different from the results of transition metal doped Au clusters, where the planar conformation of Au clusters retains up to heptamer. The stability of Aun-1Al clusters has been analyzed based on the binding energy, second difference in energy, and the energy gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels. Based on the energetics, the Au3Al and Au5Al clusters are found to have extraordinary stability. The oxidation mechanism of Al doped Au clusters have been studied by the interaction of O2 with Al, Au, AuAl, Au3Al, and Au20Al clusters. It is found that the oxidation of Aun-1Al clusters undergoes via dissociative mechanism, albeit significant charge transfer from Al to Au. Moreover, the O2 molecule prefers to attach at the Al site rather than at the Au site. [ABSTRACT FROM AUTHOR]