Stability and properties of planar carbon clusters

A series of annular structures of Cn (3⩽n⩽31) are optimized at DFT/B3LYP/6-31G∗ theoretical level. The calculated results show that odd structures and even structures have different bonding characters and properties. NBO analyses indict that C6, C10, C14, C18, C22, C26 and C30 molecules have two big delocalized π-bonding and C8, C12, C16, C20, C24 and C28 molecules have only one big delocalized π-bonding. C4 has aromaticity for it has different conformation which makes it have special bonding character. In addition, linear Cn structures are calculated to further investigate the nature of annular Cn structures.