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 Au(n-1) clusters (n=2-7,21) and (ii) the interaction of O(2) 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 Au(n-1)Al 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 Au(n-1)Al 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 Au(3)Al and Au(5)Al clusters are found to have extraordinary stability. The oxidation mechanism of Al doped Au clusters have been studied by the interaction of O(2) with Al, Au, AuAl, Au(3)Al, and Au(20)Al clusters. It is found that the oxidation of Au(n-1)Al clusters undergoes via dissociative mechanism, albeit significant charge transfer from Al to Au. Moreover, the O(2) molecule prefers to attach at the Al site rather than at the Au site.