Excited state calculation for free-base and metalloporphyrins with the partially renormalized polarization propagator approach

Free-base porphyrin and its derivatives have been attracting chemical interests with regard to their characteristic spectral behavior, showing two specific peaks called B- and Q-bands. In this Letter, a modification on the second order polarization propagator scheme is developed and the performance for porphyrin derivatives is examined. The modification is based on Dykstra and Davidson’s partial renormalization technique in terms of the coupled-pair functional aspect and has significant resistance to the quasi-degeneracy. As a consequence, the improved scheme shows encouraging results compared with the other theoretical values as well as the experimental data.