"Electronic excitations in Si and Ge nanocrystals: Parameterfree calculations",
F. Bechstedt, H.-Ch.Weissker, L.E. Ramos, and J. Furthmüller,
phys. stat. sol. (c) 1, S163 (2004).

We describe the modeling of free and oxidized Si and Ge nanocrystals with up to 363 group-IV atoms using the density-functional theory and a supercell method. Electronic excitations are described within the picture of independent Kohn-Sham particles and the delta-SCF method. Matrix elements are computed by means of projector-augmented waves. We discuss the influence of several effects such as quantum confinement, structural relaxation, strain, alloying, and oxidation.