Electronic structure and stability of anionic AuGen (n = 1–20) clusters and assemblies: a density functional modeling

Abstract

In the present study electronic structure and stabilities of cationic gold-doped germanium clusters, AuGen (n = 1 to 20), and their assemblies have been investigated by density functional theory (DFT) modeling. Computational results show a good relationship between the thermodynamic parameters, average binding energy, embedding energy, fragmentation energy, etc., with the percentage hybridization between different Ge 4s, Ge 4p, and Au 5d atomic orbitals, which plays a dominating role in the stabilization of anionic AuGe7, AuGe10, Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 clusters. Other thermodynamic and chemical parameters are also found consistent with the observed thermodynamic stabilities of the nanoclusters. In smaller size range (n < 11), Au atom always absorbs on the surface or vertex of pure Ge cluster. From n = 11, endohedral doping starts. In the assembled clusters, Au atom play the role as a bridging atom in Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 clusters. Stability of the AuGe7, AuGe10, Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 are explained using magic number in shell-filled model and mixed (π-σ) aromatic rule. As per the symmetry and structure of AuGe12 cluster, it is comparable to a nido-cluster, and hence, its stability is explained using Wade-Mingos rule. Calculated VDE, ADE, HOMO-LUMO gap, and VIP have very close agreement with the experimental results. IR and Raman frequencies show that the vibration nature of the clusters could produce electromagnetic radiation in the far infrared region which is useful for medical applications.