Transition from direct band gap to indirect band gap in fluorinated carbon

We studied phase stability, structural properties, and electronic band structures of graphite fluorides CnF (n=1,2,...,6) using density-functional theory with local density approximation. The calculation shows that CnF with sp(3) bonding has a direct gap, when n=1 or 2. Even though CnF with n>2 has not been identified experimentally, our calculation predicts that they become an indirect gap semiconductor.