A density functional theory study of structural, electronic, optical and magnetic properties of small Ag–Cu nanoalloys

The structures and properties of 13-atom silver and copper bimetallic clusters are systematically investigated by density functional theory (DFT) in the theoretical frame of the generalised gradient approximation (GGA) exchange-collection function. Optical absorption, Raman spectra, vibrational spectra, as well as electronic and magnetic properties are calculated by DFT/GGA and semi-core pseudopotentials. The following lowest-energy structures in the 13-atom Ag–Cu clusters are obtained: cuboctahedron for pure Ag13, icosahedrons for pure Cu13, Ag1Cu12, Ag6Cu7 and Ag12Cu1; and amorphous motifs for AgmCu13−m when m = 2–5 and 7–11. Ag2Cu11, Ag7Cu6 and Ag11Cu2 are magic clusters. The Ag2Cu11 cluster exhibits high energetic stability, strong electronic stability, multipole surface plasmon resonance (SPR) mode and small dipole moment. The Ag6Cu7 cluster is a Janus-separated cluster that possesses the strongest electronic stability with a band gap of 0.424 eV and a vertical ionisation potential of 5.8417 eV. The amorphous Ag7Cu6 cluster shows an Ag–Cu alloyed motif. The blue shift of the maximum SPR peak becomes increasingly evident as silver atoms are added. All Raman and vibrational spectra exhibit many significant vibration modes within the wavenumber ranges of 0–270 and 0–306.55 cm−1, respectively. Ferroelectric and ferromagnetic behaviours are observed in the 13-atom Ag–Cu nanoalloys, indicating their new potential applications in nonlinear optical devices.