Absorption spectra and electronic structures of AumAgn (m + n = 8) clusters

The electronic structures and absorption spectra of AumAgn (m + n = 8) clusters have been investigated using time-dependent density functional response theory. We have discovered that the vertical ionization potentials, highest occupied molecular orbital level, lowest unoccupied molecular orbital level and binding energies of the most stable binary AumAgn are intermediate between those of Ag8 and Au8 clusters. The analysis of the low-energy absorption spectra shows that the dominant excitation energies and the corresponding oscillator strengths exhibit an obvious odd-even oscillation with the variation of the number of Au atoms. The odd-even oscillation character indicates that the optical properties of AumAgn can be tuned by changing the stoichiometries. The excitation of electrons to exterior atoms plays a key role in optical responses of AumAgn clusters.