C28: the smallest stable fullerene?

The relative energies of different structures of C28 have been studied by density functional theory using different exchange-correlation functionals, including two with exact exchange contributions. A fullerene structure with Td symmetry (5A2 state) is found to be by far the most stable structure, followed at 4–6 eV by a graphite sheet fragment and at 5–7 eV by a C14h ring. Other structures lie still higher in energy. An infrared spectrum of fingerprint quality has been computed for the fullerene and should enable its experimental identification.