THEORY FOR OPTICAL-ABSORPTION IN SMALL CLUSTERS - DEPENDENCE ON ATOMIC-STRUCTURE AND CLUSTER-SIZE

We present a theory which permits for the first time a detailed analysis of the dependence of the absorption spectrum on atomic structure and cluster size. Thus, we determine the development of the collective excitations in small clusters and show that their broadening depends sensitively on the atomic structure, in particular at the surface. Results for Hg(n)+ clusters show that the plasmon energy is close to its jellium value in the case of spherical-like structures, but is in general between omega(p)/square-root 3 and omega(p)/square-root 2 for compact clusters. A particular success of our theory is the identification of the excitations contributing to the absorption peaks.