Density functional theory based configuration interaction calculations on the electronic spectra of free-base porphyrin, chlorin, bacteriochlorin, and cis- and trans-isobacteriochlorin

Configuration interaction calculations with single excitations based on density Functional theory (DFT/SCI) provide a reasonably accurate description of the electronic spectra of prototype porphyrin-type molecules at modest computational cost, The calculations reproduce the experimentally observed Q-B energy splitting, differences in Q and B oscillator strengths, and the intensification, relative to porphyrin, of Q(x) bands of hydroporphyrins. In all cases, the DFT/SCI results are in comparable or better agreement with experiment, compared to recent nb initio CASPT2, SAC-CL, and STEOM-CCSD calculations.