Super-valence phenomenon of carbon atoms in C20 molecule

Fourteen structures of C20 are studied at DFT/B3LYP/6-31G* theoretical level. Except ring, bowl, cage and isomer 1 which have been studied before, other isomers have not been reported so far. Calculated results show that the ring has the lowest energy at this level and isomers 1, 2, 3 and 4 have lower energies than that of cage. Analyses of optimized bond lengths, electronic structure indicate that some carbon atoms express super-valence property. In addition, NICS value is consistent with molecular orbital character in denoting aromaticity of C20 molecule. Delocalization character averts influence of curvature strain, which can well explain the stability of the cage.