  Hydrogenated silicenes possess peculiar properties owing to the strong H-Si
bonds, as revealed by an investigation using first principles calculations. The
various charge distributions, bond lengths, energy bands, and densities of
states strongly depend on different hydrogen configurations and concentrations.
The competition of strong H-Si bondings and weak sp3 hybridization dominate the
electronic properties. Chair configurations belong to semiconductors, while the
top configurations show a nearly dispersionless energy band at the Fermi level.
Both two systems display H-related partially flat bands at middle energy, and
recovery of low-lying \pi bands during the reduction of concentration. Their
densities of states exhibit prominent peaks at middle energy, and the top
systems have a delta-funtion-like peak at E=0. The intensity of these peaks are
gradually weakened as the concentration decreases, providing an effective
method to identify the H-concentration in scanning tunneling spectroscopy
experiments.
