Crystal structures and electronic properties of haloform-intercalatedC60

Using density-functional methods, we calculated structural and electronic properties of bulk chloroform- and bromoform-intercalated C 6 0 ,C 6 0 .2CHX 3 (X=Cl, Br). Both compounds are narrow-band insulator materials with a gap between valence and conduction bands larger than 1 eV. The calculated widths of the valence and conduction bands are 0.4-0.6 eV and 0.3-0.4 eV, respectively. The orbitals of the haloform molecules overlap with the π orbitals of the fullerene molecules, and the p-type orbitals of halogen atoms significantly contribute to the valence and conduction bands of C 6 0 .2CHX 3 . Charging with electrons and holes turns the systems to metals. Contrary to expectation, 10-20% of the charge is on the haloform molecules and is thus not completely localized on the fullerene molecules. Calculations on different crystal structures of C 6 0 .2CHCl 3 and C 6 0 .2CHBr 3 revealed that the density of states at the Fermi energy are sensitive to the orientation of the haloform and C 6 0 molecules. At a charging of three holes, which corresponds to the superconducting phase of pure C 6 0 and C 6 0 .2CHX 3 , the calculated density of states (DOS) at the Fermi energy increases in the sequence DOS (C 6 0 )