The self‐consistent charge density functional tight‐binding theory study of carbon adatoms using tuned Hubbard U parameters

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, the electronic structure of C61 formed by fullerene C60 with a carbon adatom is analyzed, 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. For the magnetic system C61, the HOMO‐LUMO gap can be significantly improved by appropriate forms of DFTB + U correction. U(FLL) correction can gradually lower the energy of HOMO and slightly increase the energy of LUMO, U(pSIC) can decrease all orbital energies both occupied and unoccupied states.