The electronic and molecular structure of C6: Complete active space self-consistent-field and multireference configuration interaction

Energies and equilibrium geometries have been calculated for different structures of the C6 molecule, using multiconfiguration self-consistent-field (MCSCF) and multireference configuration interaction (MRCI) methods with large basis sets of ANO type. The ground state is linear with a cumulene-like electronic structure of 3Σ−g symmetry. This result is consistent with recent experimental findings, but disagrees with other recent ab initio calculations using perturbation methods.