  DFT calculations of the electronic structure of graphane and
stoichiometrically halogenated graphene derivatives (fluorographene and other
analogous graphene halides) show (i) localized orbital basis sets can be
successfully and effectively used for such 2D materials; (ii) several
functionals predict that the band gap of graphane is greater than that of
fluorographene, whereas HSE06 gives the opposite trend; (iii) HSE06 functional
predicts quite good values of band gaps w.r.t benchmark theoretical and
experimental data; (iv) the zero band gap of graphene is opened by
hydrogenation and halogenation and strongly depends on the chemical composition
of mixed graphene halides; (v) the stability of graphene halides decreases
sharply with increasing size of the halogen atom - fluorographene is stable,
whereas graphene iodide spontaneously decomposes. In terms of band gap and
stability, the C2FBr, and C2HBr derivatives seem to be promising materials,
e.g., for (opto)electronics applications, because their band gaps are similar
to those of conventional semiconductors, and they are expected to be stable
under ambient conditions. The results indicate that other fluorinated compounds
(CaHbFc and CaFbYc, Y = Cl, Br, I) are stable insulators.
