  We explore the collective electromagnetic response in atomic clusters of
various sizes and geometries. Our aim is to understand, and hence to control,
their dielectric response, based on a fully quantum-mechanical description
which captures accurately their relevant collective modes. The electronic
energy levels and wave functions, calculated within the tight-binding model,
are used to determine the non-local dielectric response function. It is found
that the system shape, the electron filling and the driving frequency of the
external electric field strongly control the resonance properties of the
collective excitations in the frequency and spatial domains. Furthermore, it is
shown that one can design spatially localized collective excitations by
properly tailoring the nanostructure geometry.
