  The significant halogenation effects on the essential properties of graphene
are investigated by the first-principles method. The geometric structures,
electronic properties, and magnetic configurations are greatly diversified
under the various halogen adsorptions. Fluorination, with the strong
multi-orbital chemical bondings, can create the buckled graphene structure,
while the other halogenations do not change the planar {\sigma} bonding in the
presence of single-orbital hybridization. Electronic structures consist of the
carbon-, adatom- and (carbon, adatom)-dominated energy bands. All halogenated
graphenes belong to hole-doped metals except that fluorinated systems are
middle-gap semiconductors at sufficiently high concentration. Moreover, the
metallic ferromagnetism is revealed in certain adatom distributions. The
unusual hybridization-induced features are clearly evidenced in many van Hove
singularities of the density of states. The structure- and adatom-enriched
essential properties are compared with the measured results, and potential
applications are also discussed.
