A screened potential molecular-orbital calculation of the π-electron system of porphyrin

The excitation energies and oscillator strengths of the excited states of metal-free porphin were calculated by the screened potential which incorporates instantaneous polarization effects in the molecular Hartree–Fock field. The spectrum of the lowest excited states was reproduced without any use of empirical parameters. The energies of the lowest triplet 1 3B2u and singlet Q states were reproduced fairly well, while the B states were predicted to lie slightly higher than observed.