title: Study of electronic spectra of free-base porphin and Mg-porphin: comprehensive comparison of variety of ab initio, DFT, and semiempirical methods.
abstract: SAC (symmetry adapted cluster)/SAC-CI and CASPT2 (multiconfigurational second-order perturbation theory) electron excitation spectra of free-base porphin and magnesium-porphin were determined using basis set functions augmented by both the polarization and diffuse functions-6-31+G(d). Such basis is recommended for correct description of the spectra because diffuse functions play fundamental roles in the formation of Rydberg MOs. The obtained results indicated that already the lowest roots in A(u), B(1u), B(2g), and B(3g) irreducible representations display Rydberg character. The calculated spectra are in a good agreement with both experimental and recently calculated electronic transitions. It is concluded that the SAC/SAC-CI level spectral lines are significantly affected by configuration selection when energy thresholds 5.0 x 10(-6) and 5.0 x 10(-7) a.u. are used for the determination of ground and excited state properties.
authors.affiliation: Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague 2, Czech Republic.
authors.forename: Josef
authors.initials: J
authors.lastname: Seda
authors.forename: Jaroslav V
authors.initials: JV
authors.lastname: Burda
authors.forename: Jerzy
authors.initials: J
authors.lastname: Leszczynski