Tomohiro Hashimoto

Theoretical study of the valence π→π* excited states of polyacenes: Benzene and naphthalene

Multireference perturbation theory with complete active space self‐consistent field (CASSCF) reference functions was applied to the study of the valence π→π* excited states of benzene and naphthalene. The eigenvectors and eigenvalues of CASSCF with valence π active orbitals satisfy pairing properties for the alternant hydrocarbons to a good approximation. The excited states of polyacenes are classified into the covalent minus states and ionic plus states with the use of the alternancy symmetry. The present theory satisfactorily describes the ordering of low‐lying valence π→π* excited states. The overall accuracy of the present approach is surprisingly high. We were able to predict the valence excitation energies with an accuracy of 0.27 eV for singlet u states and of 0.52 eV or better for singlet g states of naphthalene. Our predicted triplet states spectrum provides a consistent assignment of the triplet–triplet absorption spectrum of naphthalene. For benzene we were able to predict the valence excitatio...

Theoretical study of the excitation spectra of five‐membered ring compounds: Cyclopentadiene, furan, and pyrrole

Multireference perturbation theory with complete active space self‐consistent field (CASSCF) reference functions was applied to the study of the valence and Rydberg excited states in the range of 5–8 eV of five‐membered ring compounds, cyclopentadiene, furan, and pyrrole. The spectra of these molecules have been studied extensively for many years but characterization is far from complete. The present approach can describe all kinds of excited states with the same accuracy. The calculated transition energies are in good agreement with corresponding experimental data. We were able to predict the valence and Rydberg excited states with an accuracy of 0.27 eV or better except for the B+2 of pyrrole. The valence excited states of five‐membered ring compounds were interpreted in terms of the covalent minus states and ionic plus states of the alternate symmetry. The unobserved 1A1→A−1 transition with very weak intensity, which is hidden under the strong 1A1→B+2 transition, is also discussed. Overall, the present...

Theoretical study of the electronic ground state of iron(II) porphine

Abstract Ten low-lying electronic states of Fe(II)-porphine, the 5 A 1 g , 5 E g , 5 B 2 g , 3 A 2 g , 3 B 2 g , 3 E g ( A ) , 3 E g ( B ) , 1 A 1 g , 1 B 2 g and 1 E g states, are studied with multireference Moller–Plesset perturbation theory with complete active space self-consistent field (CASSCF) reference functions. Triplet and singlet states are significantly multiconfigurational in character. The ten low-lying states are computed to be within a 2 eV span and the 5 A 1 g state is predicted to be the lowest. At the CASSCF level, all the quintet states are lower in energy than the triplets. This tendency is reversed, except for the 5 A 1 g state, after perturbation theory is applied. Among controversial candidates for the triplet ground state, the 3 E g state is computed to be more stable, by 0.18∼0.23 eV, than the 3 A 2 g and 3 B 2 g states.

Multireference Møller-Plesset perturbation treatment for valence and Rydberg excited states of benzene

Abstract State-specific multireference Moller-Plesset perturbation theory has been applied to the study of valence and Rydberg excitation energies of benzene. The results compare well with experiment. The calculated valence π-π ∗ excitation energies (experimental values in parentheses) are 1 B 2u , 4.77 (4.90), 1 B 1u , 6.98 (6.20), 1 E 1 u , 6.98 (6.94) and 1 E 2g , 7.88 (7.80) eV . Results of similar accuracy are obtained for the valence triplet excited states. The Rydberg excitation energies are also predicted with an accuracy of 0.18 eV or better.

Comment on Dunning's correlation-consistent basis sets

The contraction in Dunnings correlation-consistent basis sets follows the original Raffenetti approach that uses (a) occupied SCF orbitals plus (b) uncontracted primitives. Without any loss of energy, (b) can be excluded from (a), leading to substantial savings of Cce:simple-paraU times for integral-limited computing steps such as SCF gradient geometry searches on large to very large molecules.

CONTRACTED OR UNCONTRACTED POLARIZATION FUNCTIONS? COMMENT ON DUNNING'S CORRELATION-CONSISTENT BASIS SETS

Abstract For the sake of computational economy, the polarization functions given by Dunning are contracted by multiconfigurational SCF calculations for H, B, C, N, O, F and Ne atoms. For the first-row atoms, B through Ne, the generated contracted polarization functions are ( 2 d 1 d ) and ( 3 d 2 d ) and for H they are ( 2 p 1 p ), ( 3 p 1 p ), and ( 3 p 2 p ) where the numbers before and after the slash are the numbers of uncontracted and contracted polarization functions. Numerical examples on some diatomic molecules and benzene illustrate a large improvement in going from ( 1 d 1 d to ( 2 d 1 d ) for various molecular properties.