Qing-Bo Yan, Qing-Rong Zheng, and Gang Su*

College of Physical Sciences, Graduate UniVersity of Chinese Academy of Sciences, P.O. Box 4588,
Beijing 100049, China
ReceiVed: August 2, 2006; In Final Form: October 19, 2006

Abstract:

    A systematic first-principles study within density functional theory on the geometrical structures and electronic properties of unconventional fullerene C ₆₄ and its derivatives C ₆₄ X ₄ （X =H, F, Cl, Br) has been performed. By searching through all 3465 isomers of C ₆₄ , the ground state of C ₆₄ is found to be spherical shape with D ₂ symmetry, which differs from the parent cage of the recently synthesized C ₆₄ H ₄ that is pear-shaped with C _3V symmetry. We found that the addition of the halogen atoms like F, Cl, and Br to the pentagon-pentagon fusion vertex of C ₆₄ cage could enhance the stability, forming the unconventional fullerenes C ₆₄ X ₄ . The Mulliken charge populations, LUMO-HOMO gap energies, and density of states are calculated, showing that different halogen atoms added to C ₆₄ will cause remarkably different charge populations of the C ₆₄ X ₄ molecule; the chemical deriving could enlarge the energy gaps and affect the electronic structures distinctly. It is unveiled that C ₆₄ F ₄ is even more stable than C ₆₄ H ₄ , as the C-X bond energy of the former is higher than that of the latter. The computed spectra of C ₆₄ H ₄ molecules agree well with the experimental data; the IR, Raman, and NMR spectra of C ₆₄ X ₄ (X = F, Cl, Br) are also calculated to stimulate further experimental investigations. Finally, it is uncovered by total energy calculations that C ₆₄ X ₄ could form a stable hexagonal monolayer.