Electronic and optical properties in graphane

We develop the tight-binding model to study electronic and optical properties of graphane. The strong chemical bondings among the carbon and hydrogen atoms induce a special band structure and thus lead to the rich optical excitations. The absorption spectrum hardly depends on the direction of electric polarization. It exhibits a lot of shoulder structures and absorption peaks, which arise from the extreme points and the saddle points of the parabolic bands, respectively. The threshold optical excitations, only associated with the and orbitals of the carbon atoms, are revealed in a shoulder structure at 3.5 eV. The first symmetric absorption peak, appearing at 11 eV, corresponds to energy bands due to the considerable hybridization of carbon orbitals and H 1s orbitals. Also, some absorption peaks at higher frequencies indicate the bonding of and orbitals. These results are in sharp contrast to those of the graphene systems.