Dipole excitations of closed-shell alkali-metal clusters

Excitation energies and associated oscillator strengths for dipole-excited states of alkali-metal clusters--treated as jellium spheres--are calculated in the random-phase approximation (RPA). Closed-shell systems with 8, 20, 34, 40, 58, and 92 delocalized electrons are considered. The ground state is described in the Hartree-Fock (HF) approximation. The excitation spectrum is determined by solving the RPA equations. Exchange contributions are taken into account completely. The theoretical oscillator-strength distribution is found to be very different for neutral and charged clusters. Static polarizabilities of the clusters are calculated and compared with experimental values and with other calculations.