  To overcome the limitations of graphene due to lack of intrinsic band gap, it
is generally functionalized with hydrogen or halogen atoms such as fluorine and
chlorine. Generally, such functionalization yields a moderate- to high-band-gap
material in case of 100% coverage, for example ~1.5 eV in graphene
functionalized with chlorine atoms or chlorographene. In this paper, using ab
initio calculations, we report very interesting transformations observed in
chlorographene under external strain, driving it to a state with nearly
vanishing band gap (under tensile strain) and even converting it to a metal
(under compressive strain). We also show the importance of spin-orbit coupling,
responsible for the few meV band gap of chlorographene observed under high
tensile strain, which would have been a gapless semimetal otherwise.
