Doping and electronic properties of Au5-xMx (M=Ag or Cu; x = 0 to 5) nanoclusters

Abstract

A density functional theory (DFT)-based study has been performed to investigate the effect of substitutional silver (Ag) and copper (Cu) doping on the structural, electronic, magnetic, and reactivity properties of Au₅ nanoclusters. Multiple initial geometries of bimetallic Au_5-xM_x (M = Ag, Cu; x = 1–4) are optimized, and the most stable ground-state structure for each composition is selected for further studies. The impact of dopant concentration on binding energy per atom, vertical ionization potential (VIP), vertical electron affinity (VEA), chemical hardness, frontier molecular orbital gap, dipole moment, Fukui functions, nuclear independent chemical shift (NICS), density of states (DOS), IR frequencies and spin densities is systematically examined. The study found Ag doping leads to a gradual reduction in binding energy and chemical hardness, indicating increased softness and moderate reactivity. In contrast, Cu incorporation enhances s–d hybridization, strengthens metal–metal interactions, and increases stability. Fukui function results show reasonable agreement with electrostatic potential (ESP) maps in predicting nature of reactive sites. NICS analysis reveals aromatic character in the order Au₅ > Cu₅ > Ag₅. Mulliken spin populations indicate symmetry-dependent spin delocalization. DOS analysis further highlights composition-dependent changes in SOMO character. The study highlights substitutional doping as an effective strategy for tuning the stability, electronic structure, and reactivity of small gold-based bimetallic nanoclusters.