  Different stoichiometric configurations of graphane and graphene fluoride are
investigated within density functional theory. Their structural and electronic
properties are compared, and we indicate the similarities and differences among
the various configurations. Large differences between graphane and graphene
fluoride are found that are caused by the presence of charges on the fluorine
atoms. A new configuration that is more stable than the boat configuration is
predicted for graphene fluoride. We also perform GW calculations for the
electronic band gap of both graphene derivatives. These band gaps and also the
calculated Young's moduli are at variance with available experimental data.
This might indicate that the experimental samples contain a large number of
defects or are only partially covered with H or F.
