Yasuyo Hatano

Theoretical Study of Dielectric Saturation in Molecular Solutions by the Monte Carlo Simulation

By using a spherical hard core model, Monte Carlo simulation study has been made on physico-chemical properties of the dielectric saturation taking place in polar solvents surrounding a charged molecule. The strength of the dielectric saturation has been evaluated by the magnitude of the free energy curvature as a function of the polarization in the radial direction. Detailed analysis is made on the problem how the dielectric saturation shell-width and its strength change, depending on the valency (magnitude of the charge) of the solute molecule and on the dipole moment of the solvent molecule as well as on the radii of solute and solvent molecules. Based on these results, we conclude that the dielectric saturation is a considerably universal phenomenon which occurs in various molecular systems.

Monte Carlo simulation study on reorganization energy of electron-transfer reactions in polar solution

Abstract The reorganization energy of electron-transfer reactions as a function of the distance between donor and acceptor molecules is calculated by Monte Carlo simulation. It is found that the reorganization energy of charge-separations reactions is appreciably different from that of charge-recombination reactions. The average of these values agrees very well with the value obtained by a mean-spherical-approximation theory.

Monte Carlo Simulation Study of Free Energy Curves for Electron Transfer Reactions in Polar Solutions by considering the Electronic Polarizability

Abstract We have conducted Monte Carlo simulations of polar solutions with a spherical hard core model by properly taking into account the electronic polarizability of solvent molecules. We have calculated the free energy curve as a function of the reaction coordinate of electron transfer reactions in cases where the reactant is neutral and charged. From the analysis of the free energy curvature ratio between the two cases, we have found that the electronic polarizability contributes to enhance the non-linear response of solvent polarizations and that this enhancement is greatly strengthened if the translational motion of solvent molecules is frozen.

Monte Carlo simulation study on energy-gap dependence of electron-transfer reactions in polar solution : effect of electronic polarizability of solvent

Abstract We conducted Monte Carlo simulations of polar solutions by explicitly treating the effect of electronic polarizability of solvent molecules. Based on these data, we calculated the energy-gap dependence of electron-transfer rates. It was found that a considerable asymmetry of the energy-gap dependence of the charge-separation rate is brought about by the electronic polarizability. It was also found that the inverted region of the charge-recombination reaction shifts considerably to the smaller energy gap from that of the charge-separation reaction, due to the non-linearity of solvent polarization.

EXCITED STATE DYNAMICS OF RETINAL PROTEINS AS STUDIED BY FOURIER TRANSFORM OF OPTICAL ABSORPTION SPECTRUM—I. DEVELOPMENT OF ANALYTICAL METHOD

Abstract— We significantly improved the analytical method for the study of excited state dynamics of pigments, by means of the time correlation function (tcf) of the vibrational wavepacket which is produced by the Fourier transform of experimentally obtained optical absorption spectra (FTOA). Applying the tcf method to the spectra of rhodopsin at 0°C and ‐180°C, we observed specific peaks which are slightly different between 0°C and ‐180°C in the early time region (1–130 fs) of the absolute value of tcf, representing a characteristic propagation of the wavepacket along a reaction coordinate pertinent to the cis‐trans photoisomerization of the chromophore accompanying the motion of protein moiety. From the analysis of phase angle propagation, we obtained a rather small relaxation energy, 6–7 kcal/mol. Based on these results, we can say that FTOA analysis is useful as one of the most powerful techniques for the study of very early procedures in the excited state dynamics of pigments.

Characterization of molecular orbitals by counting nodal regions

The number of nodal regions can be used as an index for characterizing molecular orbitals. A computer program has been developed to count the number of nodal regions, based on the labeling and contraction algorithms. This program is applied to the water molecule, the hydrogen sulfide molecule, the hydrogen atomic orbitals, the Rydberg excited states of ethylene, dissociation of carbon monoxide, and CASSCF calculations of formaldehyde. Because the number of nodal regions is independent of the coordinate system, the method is applicable even when the molecular structure changes drastically as in bond rotation or bond elongation. Changes of nodal regions with bond elongation are investigated for carbon monoxide. A prescription for problems arising with basis set expansion techniques is also given.

Analysis of the temperature dependence of femtosecond excited state dynamics of bacteriorhodopsin by spin-boson model

Abstract The spin-boson model was applied to analyze the temperature dependence of excited state dynamics for the cis-trans photoisomerization of the chromophore in bacteriorhodopsin which was obtained by the Fourier transform of the optical absorption spectrum. The results indicate that the model is valid in the short time region less than about 30 fs and that the excited state dynamics in the time region larger than 30 fs is dominated by the non-harmonic slow vibrational motion, which is temperature independent. It is suggested that this specific vibrational motions might reflect the ultrafast cis-trans isomerization of the chromophore as well as conformation change of the protein environment.

Numerical evaluation of Goursat’s infinite integral

The infinite integral

Monte Carlo Simulation Study on the Structure and Reaction at Metal-Electrolyte Interface

\int_0^{\infty}x\,dx/(1+x^6\sin^2x)

EXCITED STATE DYNAMICS OF RETINAL PROTEINS AS STUDIED BY FOURIER TRANSFORM OF OPTICAL ABSORPTION SPECTRUM—II. THEORETICAL ANALYSIS OF WAVEPACKET PROPAGATION OF RHODOPSIN

converges but is hard to evaluate because the integrand f(x) = x/(1 + x6sin2x) is a non-convergent and unbounded function, indeed f(kπ) = kπ→ ∞ (k→ ∞). We present an efficient method to evaluate the above integral in high accuracy and actually obtain an approximate value in up to 73 significant digits on an octuple precision system in C++.