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A quasidegenerate perturbation theory based on multiconfigurational self-consistent-field (MCSCF) reference functions is derived. The perturbation theory derived here is for multistate, where several MCSCF functions obtained by the state-averaged MCSCF method are used as the reference and an effective Hamiltonian is constructed by perturbation calculation. The energies of states interested in are obtained simultaneously by diagonalization of the effective Hamiltonian. An explicit formula of the effective Hamiltonian through second order is derived as well as general formalism, and is applied to calculate potential curves of the system H2, Be–H2, CO, NO, BN, and LiF. The results agree well with those of full configuration interaction or multireference single and double excitation configuration interaction methods for both the ground and the excited states. [ABSTRACT FROM AUTHOR]

Presents a derivation of the analytic energy gradients for multiconfigural self-consistent field second-order quasidegenerate perturbation theory. Reducibility of linear equations to partial differentiations; Identification of Lagrangian multipliers; Calculation of the gradients using linear equations.

Studies a complete active space self-consistent field wave function transformed into a valence bond type representation built for nonorthogonal orbitals. Construction of the orbitals using Ruedenberg's projected localization procedure; Valence bond structures; Orbitals constituting the wave functions closest to the concept of the oldest valence bond method.

The excitation energy of Brooker's merocyanine in water-methanol mixtures shows nonlinear behavior with respect to the mole fraction of methanol, and it was suggested that this behavior is related to preferential solvation by methanol. We investigated the origin of this behavior and its relation to preferential solvation using the three-dimensional reference interaction site model self-consistent field method and time-dependent density functional theory. The calculated excitation energies were in good agreement with the experimental behavior. Analysis of the coordination numbers revealed preferential solvation by methanol. The free energy component analysis implied that solvent reorganization and solvation entropy drive the preferential solvation by methanol, while the direct solute-solvent interaction promotes solvation by water. The difference in the preferential solvation effect on the ground and excited states causes the nonlinear excitation energy shift. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Solvent and substituent effects on the absorption spectra of Brooker's merocyanine (BM) are investigated using the three-dimensional reference interaction site model self-consistent field method and time-dependent density functional theory. The π-π* excitation energies are computed for BM and its derivative 2,6-di- tert-butyl (di- t-Bu) BM. The behaviors of the computed excitation energies with increasing solvent polarity are in good agreement with those of the corresponding experimental measurements. In addition, analysis of the solute-solvent interaction energies and spatial distribution functions reveals that the effects of the solvent on the absorption spectra are reduced by the steric hindrance of the t-Bu groups. Furthermore, from the difference in the solute-solvent interaction energies of BM and di- t-Bu BM, it is shown that the effect of the t-Bu substituents on the absorption spectrum is greater in high-polarity solvents. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Changes in the acid dissociation constant, p K a, of p -carboxybenzeneboronic acid (PCBA) upon complex formation with monosaccharide are considered by using the three-dimensional reference interaction site model self-consistent field theory. The p K a of PCBA is lowered through complex formation, which is consistent with experimental observations. Free energy component analysis of the dissociation reaction was performed to investigate the details of the contribution to the p K a shift. The magnitudes of the changes in both the electronic energy and the solvation free energy were smaller for the PCBA-complex than for PCBA. These smaller changes can be attributed to the delocalization of the excess charge and to a reduction of the solvent-accessible area near the boric acid group because of the steric bulk of the monosaccharide. [ABSTRACT FROM AUTHOR]

The salt effect on the intramolecular proton transfer reaction of glycine in aqueous NaCl solution was considered using the reference interaction-site model self-consistent field theory. The free energy profiles were computed for various salt concentrations. The set of profiles clearly showed that the free energy gap between the zwitterionic form (ZW) and the neutral form (NF) became larger as the NaCl concentration increased. The transition-state structure of the solute glycine approaches the NF structure, and the reaction barrier height is reduced. From the energy decomposition analysis of the free energy of solvation, we found that the changes in the solvation free energy are determined by the balance between the electronic distortion energy, the electrostatic interaction, the solvent reorganization, and the entropic effects caused by the NaCl addition. The salt effect of NaCl makes all the species associated with the reaction unstable; however, the destabilization of NFs caused by NaCl addition is stronger than that of ZWs. In the ZW, the penalty coming from the solvent reorganization and the entropic effects are compensated by the strong solute–solvent electrostatic interaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polarizable solvent model is introduced to hybrid electronic structure theory. • Electronic polarization of both solute and solvent molecules can be handled. • High-level computation of solute electronic structure and thermodynamics is enabled. • Polarizable solvent model is introduced to hybrid electronic structure theory. The three-dimensional reference interaction-site model self-consistent field (3D-RISM-SCF) theory is an electronic structure theory of solvated molecules, which can handle the electronic polarization of the solute molecule induced by the interaction with the solvent, whereas the electronic polarization of solvent molecules is ignored. Here, the solvent-polarizable model is implemented to take into account the electronic polarization of solvent molecules. It is applied to the water molecule in an aqueous solution and the p -nitroaniline molecule in an aqueous solution, and the effects of the solvent polarization on the properties of these solutes are demonstrated. [ABSTRACT FROM AUTHOR]

The three-dimensional reference interaction-sitemodel self-consistent-field (3D-RISM-SCF) method was applied to theelectronic structure of hexahydrated chromium trication [Cr(H2O)6]3+in aqueous solution. The 3D distributionaround [Cr(H2O)6]3+showed 12 maximumdensity points arising from hydrogen bonds, as well as eight localmaximum points at the hollow sites, in the second hydration shell.The 3D distribution function also indicated 20 local maximum sitesin the third hydration shell. The low-lying excited states of verticaltransitions were computed using time-dependent density functionaltheory (TD-DFT), including the electric field from the solvent. Theelectronic configurations and excitation energies calculated usingDFT and 3D-RISM-SCF were very similar, although the orbital energiesinvolved in the transition were rather different. The two lowest excitedstates (14T and 24T) were roughly assigned tothe d–d transitions, and the third and fourth excited states(34T and 44T) were assigned to ligand-to-metalcharge-transfer transitions. The computed excited energies were ingood agreement with the experimental values. [ABSTRACT FROM AUTHOR]