PLASMONS AND EXCITONS IN MANY-ELECTRON SYSTEMS AND THE OPTICAL-RESPONSE OF ATOMIC CLUSTERS

In this paper we investigate the sensitivity of the optical response o f small atomic clusters of simple metals to the underlying approximati ons 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 partic le-hole interation dominates at all excitation energies, inhibiting th e formation of excitonic states. This result is obtained independently of the quasi-particle picture utilized. However, this picture plays a n important role in determining the resulting optical absorption profi les. Comparison with experimental data shows that simpler and traditio nal time dependent local density approximation calculations provide an accurate description of the photoabsorption phenomena in metallic clu sters.