First-principles calculations of electronic excitations in clusters

We discuss an approach to calculate electronic excitations in clusters, whi ch starts from the determination of the ground state within density functio nal theory and the local density approximation, and subsequently yields ele ctronic spectra from Green's function theory. These methods, which were ori ginally developed and used in extended systems, are shown to work well also in clusters. We discuss the theory and the computational implementation, a nd illustrate the performance and the physical mechanisms of this approach for the example clusters Na-4, Na-6, and SiH4. (C) 2000 John Wiley & Sons, Inc.