Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Oxide solid-solution catalysts, such as Zn-doped ZrO2 (ZnZrOx) and In-doped ZrO2 (InZrOx), exhibit distinctive catalytic capabilities for CH3OH synthesis via CO2 hydrogenation. We investigated the active site structures of these catalysts and their associated reaction mechanisms using both experimental and computational approaches. Electron microscopy and X-ray absorption spectroscopy reveal that the primary active sites are isolated cations, such as Zn2+ and In3+, dissolved in tetragonal ZrO2. Notably, for Zn2+, decomposition of the methoxy group, which is an essential intermediate in CH4 synthesis, is partially suppressed because of the relatively high stability of the methoxy group. Conversely, the methyl group strongly adsorbs on In3+, facilitating the conversion of the methoxy species into methyl groups. The decomposition of CH3OH is also suggested to contribute to CH4 synthesis. These results highlight the generation of CH4 as a byproduct of the InZrOx catalyst. Understanding the active site structure and elucidating the reaction mechanism at the atomic level are anticipated to contribute significantly to the future development of oxide solid-solution catalysts.

DOI： 10.1039/d4cp00635f

PubMed

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

During CO₂ hydrogenation under pressurised conditions, slight distortions were observed in the Zn structure. Our DFT calculations revealed that the adsorption of CO₂ at Zr⁴⁺ sites near Zn species can induce these structural distortions.

DOI： 10.1039/d4cy00894d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society of Applied Physics  

DOI： 10.35848/1347-4065/acc257

Scopus

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Society for Biochemistry and Molecular Biology  

DOI： 10.1016/j.jbc.2022.102763

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.jpcb.2c01971

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

The combination of experiments and simulations revealed the structural and electronic origins of Cu-doped MgAl2O4 spinel-type oxides, which we developed as the catalyst precursor for CO2-to-methanol hydrogenation. When the doping was high, elongated O–Cu octahedrally coordinated [CuO6]el was confirmed in the spinel structure. As the amount decreased, [CuO6]el was deformed to short O–Cu octahedrally coordinated [CuO6]s. Simultaneously, O atoms surrounding Cu atoms became more negatively charged, and Cu nanoparticle with a size <10 nm was formed by H2 reduction. The Cu nanoparticles derived from [CuO6]s was highly selective to CO2-to-methanol hydrogenation.

DOI： 10.1016/j.ijhydene.2022.04.295

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

DOI： 10.1246/cl.210132

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

DOI： 10.1016/j.jcrysgro.2020.125849

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACS  

DOI： 10.1021/acs.jpcb.0c05096

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

DOI： 10.1016/j.cplett.2020.137108

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

Sum-frequency generation (SFG) spectra from charged solid-liquid interfaces include significant contribution from third-order susceptibility χ(3), which mainly originates from induced water orientation in the electric double layer. We quantitatively evaluate the χ(3) susceptibility by molecular dynamics simulation in aqueous electrolyte solutions with varying concentrations and temperatures. We found that the value of χ(3) decreases with increasing concentration or temperature and that the perturbation on χ(3) is quite well-correlated with that on the dielectric constant ∈ of the solution. This correlation is understood as both quantities are commonly governed by the response of molecular orientation to the electric field. Accurate evaluation of χ(3) in various conditions is important in quantitative estimate of the third-order effect on the SFG spectroscopy, particularly in conditions of high surface charge and ion concentration.

DOI： 10.1021/acs.jpcc.8b02445

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

When sum frequency generation (SFG) spectroscopy is applied to charged solid/liquid interfaces, the observed SFG signals include both the second-order and third-order polarizations. The latter is called the χ(3) effect, which mainly includes induced molecular orientation by electric fields at charged interfaces. We theoretically evaluate the χ(3) effect on the SFG spectroscopy of liquid water using molecular dynamics (MD) simulations. The MD simulations enable us to definitely calculate the χ(3) susceptibility as a bulk property, and thereby separating it from the usual χ(2) effect shown in the SFG spectra. The calculated results of χ(3) for liquid water are fairly consistent with the experimental estimates. The present finding is utilized to analyze the spectral change of SFG at the air/water interface under electric fields and at the charged silica/water interface. The present analysis of the spectral changes allows for distinguishing the intrinsic change of the interface structure and the χ(3) effect from bulk liquid.

DOI： 10.1039/c7cp01978e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Inc  

Vibrational sum-frequency generation (vSFG) spectroscopy is used to determine the molecular structure of water at a model sea-spray aerosol surface. Both measured and calculated spectra display specific features as a result of third-order contributions to the vSFG response, and these are associated with finite interfacial electric potentials. We demonstrate that theoretical modeling enables separation of the third-order contributions, thus allowing for a systematic analysis of the strictly surface-sensitive, second-order component of the vSFG response. This study provides fundamental insights into the interfacial molecular organization and hydrogen-bonding structure of water, which mediate heterogeneous processes on sea-spray aerosols. Our results emphasize the key role that computer simulations can play in interpreting vSFG spectra and revealing microscopic details at complex aqueous interfaces, which can be difficult to extract from experiments because of the mixing of second-order, surface-sensitive, and third-order bulk-dependent contributions to the vSFG response. Generated by various sources, aerosol particles influence Earth's radiative budget and affect air quality, ecosystems, and public health. By providing a link between the oceans and the atmosphere, sea-spray aerosols play a critical yet poorly understood role in determining Earth's climate. In this study, we combine vibrational spectroscopy with computer simulations to characterize the molecular structure of model sea-spray particles. It is found that electrical potentials present at the particle surfaces generate bulk-dependent effects that modulate the spectral features. Surface-sensitive contributions are then extracted from computer simulations, allowing for an unambiguous characterization of the surface region. This information is key to the molecular-level understanding of fundamental processes, such as chemical reactions and phase transformations, which determine the ability of sea-spray particles to scatter or absorb solar radiation and promote cloud formation. Sea-spray aerosol particles have major yet poorly understood influence on the state of the atmosphere. Although non-linear vibrational spectroscopy is a reliable technique for probing the nature of aerosol interfaces, resolving the spectral features into specific structural and dynamical properties of the interface poses substantial difficulties. Here, computer simulations are used to disentangle strictly surface-sensitive contributions from bulk-dependent effects at a model sea-spray aerosol, which allows for a detailed, molecular-level characterization of the interfacial properties.

DOI： 10.1016/j.chempr.2018.04.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Sum frequency generation (SFG) spectroscopy is widely used to observe molecular orientation at interfaces through a combination of various types of polarization. The present work thoroughly examines the relation between the polarization dependence of SFG signals and the molecular orientation, by comparing SFG measurements and molecular dynamics (MD) simulations of acetonitrile/water solutions. The present SFG experiment and MD simulations yield quite consistent results on the ratios of chi((2)) elements, supporting the reliability of both means. However, the subsequent polarization analysis tends to derive more upright tilt angles of acetonitrile than the direct MD calculations. The reasons for discrepancy are examined in terms of three issues; (i) anisotropy of the Raman tensor, (ii) cross-correlation, and (iii) orientational distribution. The analysis revealed that the issues (i) and (iii) are the main causes of errors in the conventional polarization analysis of SFG spectra. In methyl CH stretching, the anisotropy of Raman tensor cannot be estimated from the simple bond polarizability model. The neglect of the orientational distribution is shown to systematically underestimate the tilt angle of acetonitrile. Further refined use of polarization analysis in collaboration with MD simulations should be proposed.

DOI： 10.1039/c6cp08856b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Difference spectroscopy between two close systems is widely used to augment its selectivity to the different parts of the observed system, though the molecular dynamics calculation of tiny difference spectra would be computationally extraordinary demanding by subtraction of two spectra. Therefore, we have proposed an efficient computational algorithm of difference spectra without resorting to the subtraction. The present paper reports our extension of the theoretical method in the isothermal-isobaric (NPT) ensemble. The present theory expands our applications of analysis including pressure dependence of the spectra. We verified that the present theory yields accurate difference spectra in the NPT condition as well, with remarkable computational efficiency over the straightforward subtraction by several orders of magnitude. This method is further applied to vibrational spectra of liquid water with varying pressure and succeeded in reproducing tiny difference spectra by pressure change. The anomalous pressure dependence is elucidated in relation to other properties of liquid water.

DOI： 10.1021/acs.jpcb.6b07121

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Measuring difference spectrum of two closely related systems is a versatile experimental method to highlight the difference in the two systems. However, the computation of a minuscule difference between two spectra by molecular dynamics' (MD) simulation is far more challenging than that of each spectrum in terms of statistical convergence. Therefore, we have proposed a theory of difference spectra, which accelerates the calculation of difference spectra by several orders of magnitude [Sakaguchi, S. et al. J. Chem. Phys. 2014, 140, 144109]. The present paper reports our subsequent advances in the computational method to greatly improve its accuracy, numerical stability, and applicability. The present method of computation based on the nonequilibrium MD simulation allows for general molecular models including polarizable ones without sacrificing its computational efficiency. The improved method was applied to polarizable liquid water and yielded difference spectra of infrared, Raman, and vibrational sum frequency generation spectroscopies. The present method enables us to analyze various difference spectra of large molecular systems using MD simulation.

DOI： 10.1021/acs.jctc.6b00697

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Traditional descriptions of vibrational energy transfer consider a quantum oscillator interacting with a classical environment. However, a major limitation of this simplified description is the neglect of quantum decoherence induced by the different interactions between two distinct quantum states and their environment, which can strongly affect the predicted energy-transfer rate and vibrational spectra. Here, we use quantum classical molecular dynamics simulations to determine the vibrational quantum decoherence time for an OH stretch vibration in liquid heavy water. We show that coherence is lost on a sub-100 fs time scale due to the different responses of the first shell neighbors to the ground and excited OH vibrational states. This ultrafast decoherence induces a strong homogeneous contribution to the linear infrared spectrum and suggests that resonant vibrational energy transfer in H2O may be more incoherent than previously thought.

DOI： 10.1021/acs.jpclett.5b02637

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The vibrational spectroscopy and relaxation of an anharmonic oscillator coupled to a harmonic bath are examined to assess the applicability of the time correlation function (TCF), the response function, and the semiclassical frequency modulation (SFM) model to the calculation of infrared (IR) spectra. These three approaches are often used in connection with the molecular dynamics simulations but have not been compared in detail. We also analyze the vibrational energy relaxation (VER), which determines the line shape and is itself a pivotal process in energy transport. The IR spectra and VER are calculated using the generalized Langevin equation (GLE), the Gaussian wavepacket (GWP) method, and the quantum master equation (QME). By calculating the vibrational frequency TCF, a detailed analysis of the frequency fluctuation and correlation time of the model is provided. The peak amplitude and width in the IR spectra calculated by the GLE with the harmonic quantum correction are shown to agree well with those by the QME though the vibrational frequency is generally overestimated. The GWP method improves the peak position by considering the zero-point energy and the anharmonicity although the red-shift slightly overshoots the QME reference. The GWP also yields an extra peak in the higher-frequency region than the fundamental transition arising from the difference frequency of the center and width oscillations of a wavepacket. The SFM approach underestimates the peak amplitude of the IR spectra but well reproduces the peak width. Further, the dependence of the VER rate on the strength of an excitation pulse is discussed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3594093]

DOI： 10.1063/1.3594093

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have performed the multistate empirical valence bond (MS-EVB) molecular dynamics simulations of a dilute hydrofluoric acid solution at ambient temperature to study the hydration structure associated with its weak acidity. The developed MS-EVB model showed reasonable agreement with experimental and previous ab initio molecular dynamics and reference interaction site model self-consistent field simulations for the free energy and structural properties. The local tetrahedral and translational order parameters around the fluorine atom significantly increase in the transition and product states of the HF dissociation reaction. This indicates that the angular and translational rearrangements of the hydrogen-bond topology are necessary especially around the fluorine atom. At the transition state of the proton transfer, the tetrahedral order parameters are very large, whereas the translational order parameters are not. This suggests that for the proton transfer to occur the large angular rearrangements of the hydrogen-bond topology are more necessary than the translational ones.

DOI： 10.1021/jp108147e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The molecular mechanisms in both vibrational relaxation and proton transfer (PT) associated with infrared (IR)-induced PT in a dilute hydrofluoric acid solution at ambient temperature are studied by molecular dynamics (MD) simulations with the multistate empirical valence bond model. To investigate the solvation dynamics, a collective solvent coordinate and its perpendicular bath modes are defined from the diabatic energy gap and their motions are examined by the generalized Langevin equation (GLE) formalism. The GLE analysis using the equilibrium MD simulation shows that the major solvent reorganizations in the PT are represented by the libration and hindered translation. In particular, the libration gives the stronger coupling to the solvent reorganization and the faster relaxation. The nonequilibrium MD simulation demonstrated that both the HF stretching vibration and the solvent reorganization relax on a similar time scale and thus compete in the PT. It also supported the "presolvation mechanism" for the PT in this system.

DOI： 10.1021/jp108413p

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The Dzyaloshinskii-Moriya (DM) interaction is induced by the spin-orbit interaction with an antisymmetric component in the exchange coupling. We have examined a possibility to detect the DM interaction as well as the non-secular part of the dipolar interaction for weakly-coupled systems by analyzing relaxation processes from the double to single quantum coherence by pulsed EPR measurement. Numerical simulation for two and three spin-1/2 systems indicates that the proposed measurement has a capability to determine the signs of the DM interactions that are important to distinguish spins in a uniform field from in a staggered field. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2008.03.074

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Venue：Nagoya University  

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