Ab initio study of the absorption spectra of Agn (n=5-8) clusters

The absorption spectra of Ag5-8 have been determined in the framework of the linear response equation-of-motion coupled cluster method and related techniques employing 11-electron relativistic effective core potential. In these treatments electron correlation effects for 11 electrons per atom are included, providing an accurate description of excited states of silver clusters. The calculations of transition energies and oscillator strengths have been carried out in a large energy interval for the stable structures and for the isomeric forms higher in energy. This allowed us to investigate the influence of structural properties on the spectroscopic patterns and to determine the role of d-electrons. Inclusion of d-electrons in the correlation treatment is mandatory to obtain accurate values for transition energies, but the excitations of s-electrons are primarily responsible for the spectroscopic patterns. They are characterized by the interference phenomena known in molecular spectroscopy which lead to a small number of intense and a large number of weak resonances. The calculated absorption spectra for the stable structures provide accurate predictions of the optical response properties in the gas phase and at the zero temperature. Since for neutral silver clusters the experimental data in the gas phase are not yet available, we also calculated spectra for deformed structures which model the influence of the environment such as rare-gas atoms, solid Ar-matrix or He-droplet. Comparison of our results with available experimental data permits us to identify structural properties responsible for the recorded spectral features. (C) 2001 American Institute of Physics.