Kazuo Toyota

Analytical energy gradient of the symmetry-adapted-cluster configuration-interaction general-R method for singlet to septet ground and excited states

A method of calculating analytical energy gradients of the singlet and triplet excited states, ionized states, electron-attached states, and high-spin states from quartet to septet states by the symmetry-adapted-cluster configuration-interaction general-R method is developed and implemented. This method is a powerful tool in the studies of geometries, dynamics, and properties of the states of molecules in which not only one-electron processes but also two- and multielectron processes are involved. The performance of the present method was confirmed by calculating the geometries and the spectroscopic constants of the diatomic and polyatomic molecules in various electronic states involving the ground state and the one- to three-electron excited states. The accurate descriptions were obtained for the equilibrium geometries, vibrational frequencies, and adiabatic excitation energies, which show the potential usefulness of the present method. The particularly interesting applications were to the C 1Ag state of acetylene, the A 2Deltau and B 2Sigmau+ states of CNC and the 4B1 and a 4Piu states of N3 radical.

Analytical energy gradients of the excited, ionized and electron-attached states calculated by the SAC-CI general-R method

A method of calculating analytical energy gradients of the excited, ionized and electron-attached states calculated by the symmetry-adapted-cluster configuration-interaction (SAC-CI) general-R method is formulated and implemented. This method is expected to be a powerful tool in the studies of dynamics and properties of molecules in which two- and multi-electron processes are involved. Good performance of this method is shown for the singlet and triplet excited states of BH and for the doublet ground and excited states of CH.

SAC-CI STUDY OF THE EXCITED STATES OF FREE BASE TETRAZAPORPHIN

Abstract The SAC (symmetry adapted cluster)/SAC-CI method is applied to calculations of the ground and excited states of free base tetrazaporphin (FBTAP). The electronic spectrum is reproduced in fairly good agreement with experiments, and unknown absorption bands in the energy region higher than 4 eV are predicted. The effect of meso-tetraaza-substitution on the excited states of porphin macrocycle explains why the compound is colored, as in the closely related compounds, phthalocyanines, used as pigments.

Elimination of singularities in molecular orbital derivatives: minimum orbital-deformation (MOD) method

We present the minimum orbital-deformation (MOD) method which effectively solves the problem intrinsic to the local approach for calculating the electron correlations. It eliminates the discontinuities in potential energy surfaces (PES) and properties, and hence the singularities of their derivatives which can occur when the localized MOs are used. The present method defines smooth invariant transformation of SCF MOs along the geometrical change, which is similar to the quasidiabatization. We demonstrate the performance of the MOD method for the ground state PES of benzene, for which artificial errors were reported in the analytical energy gradients of the local MP2.

Random-orientation high-spin electron spin resonance spectroscopy and comprehensive spectral analyses of the quintet dicarbene and dinitrene with meta-topological linkers: origins of peculiar line-broadening in fine-structure ESR spectra in organic rigid glasses.

In high-spin chemistry, random-orientation fine-structure (FS) electron spin resonance (ESR) spectroscopy entertains advantages as the most facile and convenient method to identify high-spin systems, as frequently reported in the literature. Random-orientation ESR spectroscopy applicable to organic high-spin entities can date back to the Wasserman and co-workers attempt on the first spin-quintet dicarbene, m-phenylenebis(phenylmethlene) (m-PBPM), in the 2-MTHF glass in 1963 and 1967, following their successful work on randomly oriented triplet-state ESR spectroscopy. The FS ESR spectrum of m-PBPM in the 2-MTHF glass, however, has never fully been analyzed due to a peculiar line-broadening appearing at many canonical peaks. Organic high-spin spectra from most quintet dinitrenes also suffer from similar phenomena. Seemingly intrinsic line-diffusing or -broadening phenomena adversely affect the reliable determination of FS parameters for organic high-spin entities in rigid glasses. In high-spin chemistry, the line-broadening has been an obstacle that masks key FS transitions in many cases. Thus, both the origin of the broadening and the comprehensive spectral analysis have been a long-standing issue. In this report, we examine the origin of the line-broadening appearing in the FS ESR spectra, illustrated by a comprehensive spectral analysis for m-PBPM in the quintet ground state and the first-documented quintet-state dinitrene, m-phenylenebis(nitrene) (m-PBN) in the 2-MTHF glass. A complete analysis of the random-orientation FS spectra from m-PBPM diluted in the benzophenone crystal has shown that the g-anisotropy of m-PBPM is not prominent. Also the higher-order FS terms such as S(i)(2)S(j)(2) group-theoretically allowed for S = 2 are not necessary in spite of the argument for a hydrocarbon-based tetraradical (S = 2) in the ground state. Our new approach to the line-broadening analysis invokes both exact analytical solutions for the resonance fields of canonical peaks and the magnetic-parameters gradient method. The D- and E-values of m-PBPM acquired by the spectral simulation in this study give different molecular structures of the quintet dicarbene in the benzophenone crystal lattice (D = +0.0703(0) cm(-1), E = +0.0212(0) cm(-1)) and in the 2-MTHF glass (D = +0.0780(0) cm(-1), E = +0.0221(0) cm(-1)). Microscopic origins of the line-broadening observed for high-spin oligocarbenes or oligonitrenes generated by photolysis in organic glasses have been proposed.

Time-Resolved Electron Paramagnetic Resonance and Phosphorescence Studies of the Lowest Excited Triplet States of Rh(III) Corrole Complexes

The lowest excited triplet (T(1)) ππ* states of gallium (Ga) and various rhodium (Rh) 5,10,15-trispentafluorophenyl corroles (Cors) were studied in the liquid crystal (LC) E-7 and in rigid glasses by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. The triplet sublevel energies were experimentally determined by the alignment of the molecules in the LC and by magnetophotoselection in the glass. The sublevel scheme of GaCor was determined by calculating the zero field splitting (ZFS) parameters. Axial ligand effects and quantum chemical calculations were used for the sublevel assignment of RhCors. The anisotropic EPR parameters were used to determine the important higher excited states and the magnitudes of their spin-orbit coupling (SOC) contributions were evaluated. On the basis of these results and analyses, the EPR parameters and triplet lifetime were discussed for each RhCor complex.

A quantum and deductive chemical study for all congeners of polybromo/ chlorodibenzo-p-dioxin and polybromo/chlorodibenzofuran

We have performed semiempirical quantum chemical calculations to obtain the optimized structure and the free energy (DeltaG) for all congeners (1701) of polybromo/chlorodibenzo-p-dioxins, which include all the isomers of all the homologues, and those for (3321) polybromo/chlorodibenzofurans. Then, to apply the Quantum and Deductive Chemistry Approach on the dioxin chemistry, we have carried out the multiple linear regression (MLR) as functions of temperature and the substituted numbers and positions of chlorine and bromine. The optimized structure of dibenzo-p-dioxin and the dibenzofuran ring is significantly influenced by the substitutions of the peri and lateral halogen atoms. The bond length between the aromatic ring and halogen atom also is influenced by the neighboring atoms. The bromine substitution at the 2 and 8 positions of dibenzofuran reduces the steric repulsion between the chlorine atoms at the 1 and 9 positions. The coefficients of the predicting equation of DeltaG derived by MLR suggest that the probabilities of chlorine elimination from the peri and lateral positions for polychlorodibenzo-p-dioxin are nearly equal.

Quantum Chemistry on Quantum Computers: A Polynomial-Time Quantum Algorithm for Constructing the Wave Functions of Open-Shell Molecules.

Quantum computers are capable to efficiently perform full configuration interaction (FCI) calculations of atoms and molecules by using the quantum phase estimation (QPE) algorithm. Because the success probability of the QPE depends on the overlap between approximate and exact wave functions, efficient methods to prepare accurate initial guess wave functions enough to have sufficiently large overlap with the exact ones are highly desired. Here, we propose a quantum algorithm to construct the wave function consisting of one configuration state function, which is suitable for the initial guess wave function in QPE-based FCI calculations of open-shell molecules, based on the addition theorem of angular momentum. The proposed quantum algorithm enables us to prepare the wave function consisting of an exponential number of Slater determinants only by a polynomial number of quantum operations.

Theoretical study on the electronic spectrum of TcO 4

SummaryThe theoretical electronic spectrum of TcO4− calculated by the SAC(symmetry adapted cluster)/SAC-CI method is presented. The spectrum is in good agreement with the experimental one. The observed peaks are assigned and the existence of several absorptions in the energy region higher than that observed is predicted. The difference and the similarity between the electronic spectra of TcO4− and MnO4− are clarified. The spectral difference between TcO4− and MnO4− is due to a remarkably high energy shift of the 31T2 state of TcO4−.

Efficient spontaneous 1 : 1 copolymerization of bis(ynamine)s with carbon dioxide to poly(4-pyrone)s

Spontaneous 1 : 1 copolymerization CO2 with 1,3- and 1,4-bis(N,N-diethylaminoethynyl)benzenes in the absence of a catalyst takes place to afford poly(4-pyrone)s with molecular mass Mn > 10000 and in high yield.