A time-dependent density functional theory study on the absorption spectra of Cu(n) clusters

The structures and absorption spectra of neutral Cu(n) (n = 3-9) clusters, are studied in the framework of the time-dependent density functional theory (TDDFT) using all-electron calculations. The obtained ground state structures are respectively planar for Cu(n) (n = 2-6) and 3-dimensional for Cu(n) (n = 7-9). The calculations of transition energies, oscillator strengths and dipole moment of absorption spectra have been calculated and investigated in a large energy interval, which allow us to determine the role of d electrons. The spectral analysis shows that 3d electrons are responsible for spectrum behavior of Cu(n) (n = 3-8) in addition to the contribution of 4s electrons, while only 3d electrons are primarily responsible for spectroscopic patterns of Cu9. The results are entirely different from the absorption spectra of Ag(n) with the same number of atoms.