A mechanism for the regioselective silaboration of terminal allene by a palladium catalyst has been studied theoretically. The overall reaction scheme has been examined in particular to determine the mechanism of the regioselectivity. The present catalytic reaction is exothermic and the rate-determining step is the insertion of allene into the Pd−B bond of the Pd complex. σ-Allylic and π-allylic complexes exist as intermediates and play an important role in the regioselectivity. Selective insertion of the unsubstituted C═C bond into the Pd−B bond produces the most stable σ-allylic complex, which converts to the π-allylic complex while maintaining the Pd−O coordination. The selective formation of the specific σ-allylic complex and the large activation barrier between two isomeric π-allylic complexes dominantly determines the regioselectivity of the present reaction. The major-product complex is less stable than the minor-product complex, and therefore kinetic control is predominant in the present reaction.

The excited states of a flavin-related compound, lumiflavin, were studied by the symmetry-adapted cluster (SAC)-configuration interaction (CI) method. The absorption peaks observed in the experimental spectrum were theoretically assigned. Transition energy of some low-lying n–π* states were obtained. The energy minimum structures of the first singlet and triplet excited states were calculated by the SAC-CI method. The structural changes upon excitation were at most 0.05 Å. The solvation effect on the absorption energy in aqueous solution was investigated using polarizable continuum model (PCM) and by including water molecules into the computational model. The solvatochromic shift of the second peak (31A′ state) originates from both microscopic (hydrogen bonding) and macroscopic (electronic polarization of solvent) solvation effects.

Color-tuning mechanism of Human-Blue pigment, visual color-receptor in the cone cells of the eye, has been investigated. Based on a previous Homology-modeling structure and experimental evidences, a working model was constructed, and the structure has been optimized by QM(B3LYP)/MM(AMBER) method. SAC-CI calculation was performed to obtain photo-absorption energy. The calculated absorption energy reasonably agrees with the experiment. A decomposition analysis was performed and compared with the case of Bovine rhodopsin. The electrostatic effect from the opsin is primarily important for the color-tuning. The electronic interaction (quantum effect) of the counter-residue is indispensable for quantitative calculation of the absorption energy.Color-tuning mechanism of Human-Blue pigment, visual color-receptor in the cone cells of the eye, has been investigated. Based on the SAC-CI theoretical absorption energies, a decomposition analysis was performed and compared with the case of Bovine rhodopsin. The electrostatic effect from the opsin is primary important for the color-tuning.

Symmetry-adapted cluster–configuration interaction (SAC–CI) method was applied to calculate electronic CD spectrum of a nucleoside, uridine. Based on the theoretical CD and absorption spectra, the observed peaks in the experimental spectra were assigned. The excited states of uracil, the base part of uridine, were also calculated for comparison. The origin of CD rotational strength for the low-lying π–π∗ and n–π∗ excited states was analyzed. Rotational strength of the π–π∗ transition depends on the magnitude of the electric and magnetic transition dipole moments, while that of the n–π∗ originates from the angle between the two transition moments.SAC-CI method was applied to calculate electronic CD spectrum of a nucleoside, uridine. The experimentally observed CD spectrum was assigned for the first time by comparing with the SAC-CI theoretical spectrum. The origin of CD rotational strength was analyzed and rationalized for the low-lying π–π∗ and n–π∗ excited states.

Shake-up satellite spectra accompanying the C 1s and O 1s photoelectron main lines of formaldehyde were studied by the combination of high-resolution X-ray photoelectron spectroscopy and accurate ab initio calculations. The symmetry adapted cluster–configuration interaction (SAC–CI) general-R   method finely reproduced the details of the experimental spectra and enabled quantitative assignments for the seven satellite bands: some were newly interpreted. The shake-up transitions were mainly attributed to the valence excitations accompanying the inner-shell ionization. The Rydberg excitations were found to be minor. Three-electron processes such as 1s−1n−2π*2 and 1s−1π−2π*2 were predicted in the low-energy region where the valence shake-up states such as 1s−1n–σ*, π–π* exist.

A new procedure for evaluating energy gradients in a singularity-free manner is presented for use in the SAC/SAC-CI program in which computational dimensions are reduced by the perturbation selection method. The singularity in the energy gradients stemming from a breakdown of the unitary invariance is effectively removed by the minimum orbital-deformation (MOD) method proposed in the previous study. All calculations can be done analytically via new two sets of linear equations combined with the coupled-perturbed Hartree–Fock method. Geometry optimizations for malonaldehyde in the ground and lowest singlet excited states are performed by the new method.

We present here a theoretical investigation of the mechanism of the decomposition of formic acid on perfect and defective MgO(100) surfaces using the ab initio molecular orbital method. The decomposition reaction does not occur on a perfect surface, but is feasible on defect surfaces: the surface with an O2− vacancy is more favorable than the surface with an O vacancy. Although the mechanism is different from that in the gas phase, C–H and C–O bond cleavages occur at the same time in the transition state, as in the gas phase. The carbonyl O atom moves into the vacancy to form an intermediate structure. The intermediate is more stable by 41.7 kcal mol−1 at the UMP2 level than the bridging structure. The C–H interacts with the lattice O atom to form a surface OH species. The interaction between the C–H and lattice Mg atoms is repulsive. The energy barrier is 28.3 kcal mol−1 and the overall reaction is endothermic by 48.9 kcal mol−1 at the UMP2 level.

The mechanism of the hydrogenation of CO2 to methanol on a Cu(100) surface was studied using the dipped adcluster model (DAM) combined with ab initio Hartree–Fock (HF) and second-order Møller–Plesset (MP2) calculations. The Langmuir–Hinshelwood (LH) mode, which corresponds to the reaction between coadsorbed species on the surface, was adopted. Our calculations show that hydrogen and formate are adsorbed at short-bridge sites. The coadsorption of hydrogen and CO2, in which CO2 is chemisorbed in the bent anionic state, is described well by the DAM. Five successive hydrogenations are involved in the hydrogenation of adsorbed CO2 to methanol: the intermediates are formate, dioxomethylene, formaldehyde and methoxy. The geometries of these intermediates and the transition states, as well as the energy diagrams in the reaction process, are presented. The rate-limiting step is the hydrogenation of adsorbed formate. Subsequent steps occur relatively readily, and lead to the formation of methanol. Clearly, any factor that could enhance the hydrogenation of formate on copper should lead to enhanced activity in methanol synthesis.

The SAC-CI (symmetry-adapted-cluster configuration-interaction) general-R method was used to assign the satellite peaks of the ionization spectrum of CO2. Outer-valence satellite peaks were assigned to the 2Πu and 2Πg states and inner-valence satellite peaks were assigned to the 2Σu+ and 2Σg+ states. The SAC-CI general-R method reproduces well the experimental spectrum in both the outer and inner-valence regions. On the other hand, while the SAC-CI SD-R method calculates the main peaks quite well, the shake-up states are by about 3 eV higher than those of the general-R method.