SCF-?-electron calculations using orthogonalised atomic orbitals

The non-empirical SCF-LCAO-π-electron method previously developed for closed-shell molecules is extended to treat open-shell hydrocarbon systems. It is shown that the use of the Roothaan formalism, with configuration interaction involving all singly excited states, leads to a satisfactory description of the doublet state excitation energies and of the spin density distributions. Comparison of the total π-electronic energies with values relating to the corresponding closed-shell systems yields ionisation potentials in good agreement with experimental data.