Plasmons and excitons in many-electron systems and the optical response of atomic clusters

Abstract

In this paper we investigate the sensitivity of the optical response of small atomic clusters of simple metals to the underlying approximations utilized in the calculation of their quasi-particle properties. In spite of the appreciable quasi-particle gaps induced by quantum size effects, it is found that the repulsive part of the irreducible particle-hole interation dominates at all excitation energies, inhibiting the formation of excitonic states. This result is obtained independently of the quasi-particle picture utilized. However, this picture plays an important role in determining the resulting optical absorption profiles. Comparison with experimental data shows that simpler and traditional time dependent local density approximation calculations provide an accurate description of the photoabsorption phenomena in metallic clusters.