EFFECTIVE PARTICLE-HOLE INTERACTION AND THE OPTICAL-RESPONSE OF SIMPLE-METAL CLUSTERS

Following Sham and Rice [L. J. Sham and T. M. Rice, Phys. Rev. 144, 70 8 (1966)], the correlated motion of particle-hole pairs is studied, st arting from the general two-particle Green's function. In this way, we derive a matrix equation for eigenvalues and wave functions, respecti vely, of the general type of collective excitation of an N-particle sy stem. The interplay between excitons and plasmons is fully described b y this set of equations. As a by-product we obtain - at least a poster iori - a justification for the use of the time-dependent local-density approximation for simple-metal clusters.