Structural, electronic and optical properties of 7-atom Ag-Cu nanoclusters from density functional theory

Abstract

The structures and electronic properties of 7-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-correlation functional. Optical absorption, Raman spectra, as well as vibrational spectra are calculated by DFT/GGA and semi-core pseudopotentials. The lowest-energy stable motifs are primarily related to the quantity of Cu-Cu bonds and Ag-Cu bonds. The Ag₅Cu₂ 2-I with D _5h symmetry cluster is the lowest energy cluster in the family of the 7-atom Ag-Cu nanoclusters, but has the lowest electronic stability. The Ag₅Cu₂ 2-I, Ag₄Cu₃ 3-I and Ag₃Cu₄ 4-I clusters with mixed motifs indicate that silver and copper may be miscible on the nanoscale but not in bulk. Overall, with increasing Cu atoms, for the lowest energy nanoclusters, blue-shift of the maximum absorption peaks presents in the UV-Vis wavelength range, the intensities of the maximum peak of the Raman spectra weaken, the Cu atom(s) introduced make the vibrational spectra complex, and the intensities of the vibrational spectra strengthen. The calculated vibrational and Raman spectroscopy of 7-atom Ag-Cu clusters may be helpful in determining the size and structure of the experimental cluster.