Atsushi Ishikawa

Oxygen atom transfer reactions of iridium and osmium complexes: theoretical study of characteristic features and significantly large differences between these two complexes.

Oxygen atom transfer reaction between ML(3)=O and ML(3) (L = 2,4,6-trimethylphenyl (Mes) for M = Ir and L = 2,6-diisopropylphenylimide (NAr) for M = Os) was theoretically investigated by DFT method. The optimized geometry of (Mes)(3)Ir-O-Ir(Mes)(3) agrees well with the experimental one, although those of (CH(3))(3)Ir-O-Ir(CH(3))(3) and Ph(3)Ir-O-IrPh(3) are much different from the experimental one of the Mes complex. These results indicate that the bulky ligand plays important roles to determine geometry of the mu-oxo dinuclear Ir complex. Theoretical study of the real systems presents clear pictures of these oxygen atom transfer reactions, as follows: In the Ir reaction system, (i) the mu-oxo bridged dinuclear complex is more stable than the infinite separation system in potential energy surface, indicating this is incomplete oxygen atom transfer reaction which does not occur at very low temperature, (ii) unsymmetrical transition state is newly found, in which one Ir-O distance is longer than the other one, (iii) unsymmetrical local minimum is also newly found between the transition state and the infinite separation system, and (iv) activation barrier (E(a)) is very small. In the Os reaction system, (v) the transition state is symmetrical, while no intermediate is observed unlike the Ir reaction system, and (vi) E(a) is very large. These results are consistent with the experimental results that the reaction rapidly occurs in the Ir system but very slowly in the Os system, and that the mu-oxo bridged dinuclear intermediate is detected in the Ir system but not in the Os system. To elucidate the reasons of these differences between Ir and Os systems, the E(a) value is decomposed into the nuclear and electronic factors. The former is the energy necessary to distort ML(3) and ML(3)=O moieties from their equilibrium geometries to those in the transition state. The latter depends on donor-acceptor interaction between ML(3)=O and ML(3). The nuclear factor is much larger in the Os system than in the Ir system and it contributes to about 70% of the difference in E(a). The energy gap between the donor orbital of ML(3) and the acceptor orbital of ML(3)=O is much larger in the Os system than in the Ir system, which also contributes to the lower E(a) value of the Ir system than that of the Os system.

Solving the Schrödinger and Dirac equations of hydrogen molecular ion accurately by the free iterative complement interaction method

The nonrelativistic Schrödinger equation and the relativistic four-component Dirac equation of H(2) (+) were solved accurately in an analytical expansion form by the free iterative complement interaction (ICI) method combined with the variational principle. In the nonrelativistic case, we compared the free ICI wave function with the so-called exact wave function as two different expansions converging to the unique exact wave function and found that the free ICI method is much more efficient than the exact method. In the relativistic case, we first used the inverse Hamiltonian to guarantee Ritz-type variational principle and obtained accurate result. We also showed that the ordinary variational calculation also gives a nice convergence when the g function is appropriately chosen, since then the free ICI calculation guarantees a correct relationship between the large and small components of each adjacent order, which we call ICI balance. This is the first application of the relativistic free ICI method to molecule. We calculated both ground and excited states in good convergence, and not only the upper bound but also the lower bound of the ground-state energy. The error bound analysis has assured that the present result is highly accurate.

Theoretical study of photoinduced epoxidation of olefins catalyzed by ruthenium porphyrin.

Epoxidation of olefin by [Ru(TMP)(CO)(O)](-) (TMP = tetramesitylporphine), which is a key step of the photocatalyzed epoxidation of olefin by [Ru(TMP)(CO)], is studied mainly with the density functional theory (DFT) method, where [Ru(Por)(CO)] is employed as a model complex (Por = unsubstituted porphyrin). The CASSCF method was also used to investigate the electronic structure of important species in the catalytic cycle. In all of the ruthenium porphyrin species involved in the catalytic cycle, the weight of the main configuration of the CASSCF wave function is larger than 85%, suggesting that the static correlation is not very large. Also, unrestricted-DFT-calculated natural orbitals are essentially the same as CASSCF-calculated ones, here. On the basis of these results, we employed the DFT method in this work. Present computational results show characteristic features of this reaction, as follows: (i) The epoxidation reaction occurs via carboradical-type transition state. Neither carbocation-type nor concerted oxene-insertion-type character is observed in the transition state. (ii) Electron and spin populations transfer from the olefin moiety to the porphyrin ring in the step of the C-O bond formation. (iii) Electron and spin populations of the olefin and porphyrin moieties considerably change around the transition state. (iv) The atomic and spin populations of Ru change little in the reaction, indicating that the Ru center keeps the +II oxidation state in the whole catalytic cycle. (v) The stability of the olefin adduct [Ru(Por)(CO)(O)(olefin)](-) considerably depends on the kind of olefin, such as ethylene, n-hexene, and styrene. In particular, styrene forms a stable olefin adduct. And, (vi) interestingly, the difference in the activation barrier among these olefins is small in the quantitative level (within 5 kcal/mol), indicating that this catalyst can be applied to various substrates. This is because the stabilities and electronic structures of both the olefin adduct and the transition state are similarly influenced by the substituent of olefin.

Quantum chemical approach for condensed-phase thermochemistry: Proposal of a harmonic solvation model

We propose a novel quantum chemical method, called the harmonic solvation model (HSM), for calculating thermochemical parameters in the condensed phase, particularly in the liquid phase. The HSM represents translational and rotational motions of a solute as vibrations interacting with a cavity wall of solvent molecules. As examples, the HSM and the ideal-gas model (IGM) were used for the standard formation reaction of liquid water, combustion reactions of liquid formic acid, methanol, and ethanol, vapor-liquid equilibration of water and ethanol, and dissolution of gaseous CO2 in water. The numerical results confirmed the reliability and applicability of the HSM. In particular, the temperature dependence of the Gibbs energy of liquid molecules was accurately reproduced by the HSM; for example, the boiling point of water was reasonably determined using the HSM, whereas the conventional IGM treatment failed to obtain a crossing of the two Gibbs energy curves for gaseous and liquid water.

Molecular Structure and Internal Rotation of CF3 Group of Methyl Trifluoroacetate: Gas Electron Diffraction, Microwave Spectroscopy, and Quantum Chemical Calculation Studies

The molecular structure of methyl trifluoroacetate (CF3COOCH3) has been determined by gas electron diffraction (GED), microwave spectroscopy (MW), and quantum chemical calculations (QC). QC study provides the optimized geometries and force constants of the molecule. They were used to estimate the structural model for GED study and to calculate the vibrational corrections for GED and MW data. In addition, potential energy curves for the internal rotations of CF3 and CH3 groups have been calculated for anti (dihedral angle of α(CCOC) is 180°) and syn (α(CCOC) = 0°) conformers of methyl trifluoroacetate. Both the GED and MW data revealed the existence of the anti conformer. Molecular constants determined by MW are A0 = 3613.4(3) MHz, B0 = 1521.146(8) MHz, C0 = 1332.264(9) MHz, ΔJ = 0.09(2) kHz, and ΔJK = 0.23(6) kHz. The GED data were well-reproduced by the analysis in which a large-amplitude motion of the CF3 group was taken into account. The barrier of the internal rotation of the CF3 group was determined to be V3 = 2.3(4) kJu202fmol(-1), where V3 is the potential coefficient of the assumed potential function, V(ϕ) = (V3/2)(1 - cosu202f3ϕ), and ϕ is a rotational angle for the CF3 group. The values of geometrical parameters (re structure) of the anti conformer of CF3COOCH3 are r((O═)C-O) = 1.326(6) Å, r(O-CH3) = 1.421(4) Å, r(C-H(in-plane)) = 1.083(14) Å, r(C-H(out-of-plane)) = 1.087(14) Å, r(C═O) = 1.190(7) Å, r(C-C) = 1.533(4) Å, r(C-F(in-plane)) = 1.319(4) Å, r(C-F(out-of-plane)) = 1.320(6) Å, ∠COC = 116.3(5)°, ∠OCH(in-plane) = 105.2° (fixed), ∠OCH(out-of-plane) = 110.0° (fixed), ∠O═CC = 123.7° (fixed), ∠O-CC = 111.2(5)°, ∠OCO = 125.2(5)°, ∠CCF = 110.1(3)°, and OCCF (out-of-plane dihedral angles) = ± 121.5(1)°. Numbers in parentheses are three times the standard deviations of the data fit.

XPS of Oxygen Atoms on Ag(111) and Ag(110) Surfaces: Accurate Study with SAC/SAC-CI Combined with Dipped Adcluster Model

O1s core‐electron binding energies (CEBE) of the atomic oxygens on different Ag surfaces were investigated by the symmetry adapted cluster‐configuration interaction (SAC‐CI) method combined with the dipped adcluster model, in which the electron exchange between bulk metal and adsorbate is taken into account properly. Electrophilic and nucleophilic oxygens (Oelec and Onuc) that might be important for olefin epoxidation in a low‐oxygen coverage condition were focused here. We consider the O1s CEBE as a key property to distinguish the surface oxygen states, and series of calculation was carried out by the Hartree–Fock, Density functional theory, and SAC/SAC‐CI methods. The experimental information and our SAC/SAC‐CI results indicate that Oelec is the atomic oxygen adsorbed on the fcc site of Ag(111) and that Onuc is the one on the reconstructed added‐row site of Ag(110) and that one‐ and two‐electron transfers occur, respectively, to the Oelec and Onuc adclusters from the silver surface.

Analysis on Si modified MMI-waveguide-type optical switch operated with carrier injection

Silicon modified multimode-interference(MMI)-waveguide-type 2×2 optical switch operated with carrier injection was proposed for efficient modulation by flattening the refractive index profile of the waveguide. Fundamental designing and switching characteristics were analyzed.

Performance simulation of novel silicon cross-waveguide reflection-type optical switch

We proposed a novel silicon cross-waveguide reflection-type optical switch. Performance simulation was carried out to show a low crosstalk of about -25dB. We actually fabricated the device to exhibit fundamental switching operation.

Abstract: Solving the Schrödinger and Dirac Equations of Atoms and Molecules with Massively Parallel Computer

Schrödinger and relativistic Dirac equations are the most fundamental equations in quantum mechanics and govern most phenomena in molecular material science. In spite of this importance, exact solutions of these equations have not been done for over 80 years after the discovery. However, recently, one of the authors was successful to propose a general theory of solving these equations in high accuracy. Further, the method proposed for general atoms and molecules is suitable for massively parallel computing since we introduce the sampling method that requires the local Schrödinger equation to be satisfied at all the sampled points. In this presentation, we will show some examples of applications of our method to general atoms and molecules. Our purpose is to propose accurately predictive quantum chemistry with the solutions of the Schrödinger and relativistic Dirac equations. There, the massively parallel super computing should be of much help for realizing this purpose.

Solving the Schrödinger Equation for the Hydrogen Molecular Ion in a Magnetic Field Using the Free-Complement Method

The hydrogen molecular ion (H 2 + ) in a magnetic field is investigated theoretically using the free-complement (FC) method for solving the Schrodinger equation. H 2 + was placed in magnetic fields of moderate strengths. Our results were shown to be highly accurate. Total energies, dissociation energies, quadrupole moments, and electron densities were calculated for parallel and perpendicular fields. The gauge-origin dependence of the wave function was examined in detail. It was shown that the results of the FC method are always gauge independent when the gauge-including function is employed as the initial function. Even when we start from the gauge-nonincluding functions, the FC method gives the gauge-independent result in some order, because the FC wave function becomes exact as the order of the FC calculations increases. We observed that properties such as total energy, potential energy curve, vibrational level, and electron density distribution became gauge-origin independent as the order of the FC wave function increased.