Superatomic and adsorption properties of Ni atom doped Au clusters

Abstract

Due to their strong relativistic effects, Au clusters exhibit many unusual geometric structures. Among them, Au₇⁻, Au₈ and Au₉⁺ have 18 valence electrons satisfying the magic numbers in the jellium model, respectively, but these three non-spherical clusters are not superatoms. In general, a single dopant atom can drastically change the structural and electronic properties of Au clusters. Here, we searched structures of NiAu₇⁻, NiAu₈ and NiAu₉⁺ clusters using the genetic algorithm program (GA) combined with density functional theory (DFT). It was found that the alloy clusters are all 3D spherical structures. The molecular orbitals and density of states analysis indicate that they have completely filled superatomic shells (1S²1P⁶), in which the electronic structure of the Ni atom is d¹⁰. Then, the electrostatic potential surfaces of the alloy clusters are analyzed, and the calculated results show that the NiAu₈ superatom has remarkable σ-holes with positive potential regions. Moreover, these electron-deficient regions can be considered as interaction sites with some electron donors. After a Lewis base CO gas molecule is adsorbed on the Au-based superatom, we found that the C–O bond distance becomes slightly elongated and its stretching frequency presents a significant red-shift. This is due to the fact that 5d electrons of the Au atom of the NiAu₈ transfer towards the anti-bond π orbitals of the CO molecule. Hence, this is an effective strategy for finding new types of superatoms and potential catalysts for covalent bond activation.