Configuration-interaction calculations of jellium clusters by the nuclear shell model.

Abstract

Configuration-interaction (CI) calculations are performed on Na clusters of up to 20 atoms within the spherical jellium model, with particular attention paid to the magic clusters with N=2, 8, and 20. The interacting valence electrons are assumed to move in the Coulomb field of the jellium core. The numerical work is carried out by the nuclear-structure code oxbash modified to handle LS coupling. The many-particle bases are constructed of harmonic-oscillator single-particle states extending over 11 major shells and, alternatively, of single-particle states generated by the local-spin-density approximation (LSDA). The calculated quantities include ground- and excited state energies, ionization potentials, and photoabsorption cross sections. The microscopic structure of the dominating plasmon excitation is studied in neutral and ionized clusters. Results of the LSDA, where applicable, are found to be in substantial agreement with the CI results. Convergence problems are addressed and are found hard to overcome for the larger clusters studied. Tamm-Dancoff approximation and random-phase approximation results are simulated by suitable restrictions of the CI space.