Based on ab initio density functional theory we present electronic properties and the optical response for Si nanocrystals embedded in amorphous SiO(2) networks. Quasi-spherical dots with diameters from 0.8 to 1.6 nm are investigated. The results for Si nanocrystals embedded in SiO(2) are compared with corresponding results for hydrogenated Si nanocrystals of the same size. The calculations show the influence of the interface between nanocrystal and matrix on the electronic properties. The results are compared with recent experimental data and discussed in detail. As striking features, strong reductions of the gaps and their diameter variation are predicted due to the oxide presence. Electronic confinement mainly influences the absorption edge while at higher photon energies only broad peaks at almost fixed positions occur.
