  The self-consistent charge density functional tight-binding (DFTB) theory is
a useful tool for realizing the electronic structures of large molecular
complex systems. In this study, we analyze the electronic structure of C61,
formed by fullerene C60 with a carbon adatom, using the fully localized limit
and pseudo self-interaction correction methods of DFTB to adjust the Hubbard U
parameter (DFTB+U). The results show that both the methods used to adjust U can
significantly reduce the molecular orbital energy of occupied states localized
on the defect carbon atom and improve the gap between highest occupied
molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) of C61.
This work will provide a methodological reference point for future DFTB
calculations of the electronic structures of carbon materials.
