An efficient computational approach that combines semiempirical density-functional based tight-binding method (DFTB) for geometry optimization and density-functional theory for single-point energy calculation is employed to search for the lowest-energy structures of higher fullerenes C 110 to C 120. In addition, a systematic study of low-lying structures of lower fullerenes C 38 to C 80 is undertaken. For the latter study, the targeted isomers amount to 131 164, including 17·IPR (isolated pentagon rule) isomers and all non-IPR isomers. Non-IPR isomers dominate the low-lying population of C 72 but are gradually phased out of the low-lying population when the fullerene size increases toward C 80. An unexpected manner of pentagonal adjacency was observed, that is, for fullerenes containing an adjacent-pentagon chain with less than five pentagons, the longer chain incurs less energy penalty than the shorter chain when the top-two lowest-energy fullerene cages (for all C 38 - C 70) have the same number of adjacent pentagons. For higher fullerenes C 112 to C 120, a full set of total 32 795 IPR isomers were optimized using the DFTB method. An energy cutoff value of 6.3 kcal/mol was used to collect low-lying candidate isomers for the second-stage single-point energy calculation at the DFT level. Multiple candidates for the lowest-energy structure were identified for C 112, C 118, and C 120. Among them, C 112:3299 and C 118:7308 exhibit a large HOMO-LUMO gap. For C 116, a sole candidate for the lowest-energy structure was identified, namely, C 116:6061 which has a high T h symmetry and a large HOMO-LUMO gap and is 12.5 kcal/mol lower in energy than the second lowest-energy isomer. Thus, C 116: 6061 is most likely to be isolated first in the laboratory among the five large fullerenes. 13C NMR spectra of the ten lowest-energy isomers of C 112 to C 120 were calculated for comparison with the experiment.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films