13 research outputs found
Crystal Structures and Electronic Properties of Haloform-Intercalated C60
Using density functional methods we calculated structural and electronic
properties of bulk chloroform and bromoform intercalated C60, C60 2CHX3
(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 orbitals of the
fullerene molecules and the p-type orbitals of halogen atoms significantly
contribute to the valence and conduction bands of C60 2CHX3. Charging with
electrons and holes turns the systems to metals. Contrary to expectation, 10 to
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 C60 2CHCl3 and C60 2CHBr3 revealed that the density of states at
the Fermi energy are sensitive to the orientation of the haloform and C60
molecules. At a charging of three holes, which corresponds to the
superconducting phase of pure C60 and C60 2CHX3, the calculated density of
states (DOS) at the Fermi energy increases in the sequence DOS(C60) < DOS(C60
2CHCl3) < DOS(C60 2CHBr3).Comment: 11 pages, 7 figures, 4 table
ILL experimental reports and theory college activities 1984
CNRS RP 350 (52) (1-2) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc
Chemical structural effects on γ-ray spectra of positron annihilation in fluorobenzenes
Spectra of γ-ray Doppler shifts for positron annihilation in benzene and
its fluoro-derivatives are simulated using low energy plane wave positron (LEPWP)
approximation. The results are compared with available measurements. It is found that the
Doppler shifts in these larger aromatic compounds are dominated by the contributions of
the valence electrons and that the LEPWP model overestimates the measurements by
approximately 30%, in agreement with previous findings in noble gases and small molecules.
It is further revealed that the halogen atoms not only switch the sign of the charges on
carbon atoms that they bond to, but that they also polarize other C-H bonds in the
molecule leading to a redistribution of the molecular electrostatic potentials. As a
result, it is likely that the halogen atoms contribute more significantly to the
annihilation process. The present study also suggests that, while the Doppler shifts are
sensitive to the number of valence electrons in the molecules, they are less sensitive to
the chemical structures of isomers that have the same numbers and type of atoms and,
hence, the same numbers of electrons. Further investigation of this effect is warranted