First-principles calculations of electronic excitations in clusters

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