On the structure and vibrational frequencies of C-24

Several structures of C-24 have been studied using different density functional methods. Using the B3LYP (Becke 3-parameter Lee-Yang-Parr) method, fingerprint-quality infrared spectra have been computed for all species. The computed geometries differ substantially from those obtained at the SCF level due to delocalization effects. Both ''exact-exchange'' corrections to the exchange functional and the use of different correlation functionals have significant effects on the relative energetics. Our best calculations indicate that a dodecadehydrocoronene planar sheet and a fullerene cage are comparable in energy, followed by a polyacetylenic ring and a bowl structure, At high temperatures, the ring is expected to prevail due to vibrational entropy from many low-lying vibrations.