Electronic structures of linear C 4, C 6, C 8, and C 10 carbon clusters and a symmetry breaking phenomenon

Abstract

The electronic structures of linear C 4, C 6, C 8, and C 10 carbon clusters are studied using the self-consistent-field (SCF) and single and double configuration interaction (CISD) methods in conjunction with a double-zeta plus polarization basis set. The relative energies of various electronic states and that of two distinct linear geometries, cumulenic and acetylenic, are considered. It is found that the energy difference between the lowest triplet and singlet states of the cumulenic structure and that between the cumulenic and acetylenic structures decrease monotonically as the carbon chain lengthens. For C 8 and C 10 these energy differences are very small. A symmetry breaking phenomenon is observed in the 1A g component (in D 2h) of the 1Δ g singlet state. Its symmetry-adapted, D ∞h symmetric SCF wave function is unstable and the symmetry-broken, D 2h symmetric solution has lower energy.