Search for Lowest-Energy Nonclassical Fullerenes III: C22

Abstract

Density functional and second-order Møller-Plesset perturbation (MP2) methods were employed in the investigation of low-lying C22 isomers. All cage structures with four-, five-, six-, and seven-membered rings were examined with the monocyclic ring, bowl, and other noncage structures. Cage isomers were first identified via graph theoretical methods, and noncages were identified by basin-hopping methods. Initial isomer screenings were carried out at the PBE/DND level of theory. Low-lying isomers, within 0.6 eV of the predicted lowest-energy isomer, were further evaluated at the PBE1PBE/cc-pVTZ and MP2/cc-pVTZ levels. Our results confirm that the cage structures are more stable than the ring structure and the bowl structure. The lowest-energy structure for C22 is predicted to be the C22-1 cage containing one four-membered ring. Anion photoelectron and optical spectra of the six lowest-lying isomers are also computed.