"Germanium and silicon
nanocrystals - excitation energies and compression",
H.-Ch.Weissker,
J. Furthmüller, L.E. Ramos,
and F. Bechstedt,
Physics, Chemistry And
Application of Nanostructures: Reviews And Short Notes to Nanomeeting
2005, V.E. Borisenko, S.V. Gaponenko, and
V.S. Gurin (Editors), World Scientific Publishing Company (2005), p.
62.
We calculate nanocrystal excitation energies using a Delta-SCF method with occupation constraint, thus including both self-energy and Coulomb effects. We find the well-known r-1 dependence. The energies are found to follow the pressure dependence of the relevant gaps in bulk materials. While Ge nanocrystals have a positive pressure dependence, the contrary holds for Si. For the pressure dependence of the excitation energies in SixGe1-x nanocrystals, we find the transition from Ge-like to Si-like behavior at a composition of about x=0.3.