研究者詳細 - 稲垣　泰一

稲垣　泰一（イナガキ　タイチ）

Inagaki, Taichi

写真a

所属（所属キャンパス）: 理工学部化学科（矢上）

職名: 助教

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Insights into the Luminescence Quantum Yields of Cyclometalated Iridium(III) Complexes: A Density Functional Theory and Machine Learning Approach

Hatanaka M., Kato H., Sakai M., Kariya K., Nakatani S., Yoshimura T., Inagaki T.

Journal of Physical Chemistry A （Journal of Physical Chemistry A） 127 （ 36 ） 7630 - 7637 2023年09月

ISSN 10895639

　概要を見る

Cyclometalated iridium(III) complexes have been used in various optical materials, including organic light-emitting diodes (OLEDs) and photocatalysts, and a deeper understanding and prediction of their luminescence quantum yields (LQYs) greatly aid in accelerating material design. In this study, we integrated density functional theory (DFT) calculations with machine learning (ML) techniques to extract factors controlling LQY. Although a substantial data set of Ir(III) complexes and their LQYs is indispensable for constructing accurate ML models to predict LQYs, generating this type of data set is challenging due to the complexities associated with ab initio calculations of LQYs. To address this issue, we investigated the nonradiative decay process of nine Ir(III) complexes emitting blue to green, each exhibiting varying experimental LQYs, by using DFT calculations. For all nine complexes, the quenching process was induced by the rotation of the single bond in one of the ligands, which converted the six-coordinate structure to the five-coordinate structure. Since the decay mechanism was common for the nine Ir(III) complexes, parameters correlated with LQYs could be used as objective variables instead of LQYs. Based on this idea, we collected a data set featuring Ir(III) complexes and the energy differences between their six- and five-coordinate triplet structures, which correlated with LQYs. We also constructed ML models using the calculated LQYs as the objective variables with the parameters from the ground-state calculations as explanatory variables. The analyses of the constructed model revealed that the LUMO energy of the ligand made the most significant negative contribution to LQY. This suggests that the potential energy surface of the metal-to-ligand charge transfer (MLCT) excited state, which stabilizes the six-coordinate structure, is reduced by decreasing the energy of the unoccupied orbitals.
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Anisotropic and Finite Effects on Intermolecular Vibration and Relaxation Dynamics: Low-Frequency Raman Spectroscopy of Water Film and Droplet on Graphene by Molecular Dynamics Simulations

Inagaki T., Hatanaka M., Saito S.

Journal of Physical Chemistry B （Journal of Physical Chemistry B） 127 （ 26 ） 5869 - 5880 2023年07月

ISSN 15206106

　概要を見る

The structural and dynamical properties of water can be greatly altered by the anisotropic interfacial environment. Here, we study the intermolecular vibration and relaxation dynamics of a water film and a water droplet on a graphene surface based on low-frequency Raman spectra calculated from molecular dynamics simulations. The calculated Raman spectra of the interfacial water systems show a weakened libration peak and an enhanced intermolecular hydrogen bond (HB) stretching peak compared to the spectrum of bulk water, which are attributed to softened orientation motion. We also find that the collective polarizability relaxation in the droplet is much slower than that in the film and bulk, which is completely different from the collective dipole relaxation. The slow relaxation is due to a positive correlation between the induced polarizabilities of distinct molecules caused by the global and anisotropic structural fluctuations of the water droplet. Furthermore, we find that the two-dimensional HB network by the orientation-ordered interfacial water molecules leads to different intermolecular vibration dynamics between the parallel and perpendicular components. The present theoretical study demonstrates that low-frequency Raman spectroscopy can reveal the anisotropic and finite effects on the intermolecular dynamics of the water film and droplet.
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Excited state calculations using variational quantum eigensolver with spin-restricted ansätze and automatically-adjusted constraints

Gocho S., Nakamura H., Kanno S., Gao Q., Kobayashi T., Inagaki T., Hatanaka M.

npj Computational Materials （npj Computational Materials） 9 （ 1 ） 2023年01月

　概要を見る

The ground and excited state calculations at key geometries, such as the Frank–Condon (FC) and the conical intersection (CI) geometries, are essential for understanding photophysical properties. To compute these geometries on noisy intermediate-scale quantum devices, we proposed a strategy that combined a chemistry-inspired spin-restricted ansatz and a new excited state calculation method called the variational quantum eigensolver under automatically-adjusted constraints (VQE/AC). Unlike the conventional excited state calculation method, called the variational quantum deflation, the VQE/AC does not require the pre-determination of constraint weights and has the potential to describe smooth potential energy surfaces. To validate this strategy, we performed the excited state calculations at the FC and CI geometries of ethylene and phenol blue at the complete active space self-consistent field (CASSCF) level of theory, and found that the energy errors were at most 2 kcal mol−1 even on the ibm_kawasaki device.
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A New Pathway for CO<inf>2</inf>Reduction Relying on the Self-Activation Mechanism of Boron-Doped Diamond Cathode

Du J., Fiorani A., Inagaki T., Otake A., Murata M., Hatanaka M., Einaga Y.

JACS Au （JACS Au） 2 （ 6 ） 1375 - 1382 2022年06月

　概要を見る

By means of an initial electrochemical carbon dioxide reduction reaction (eCO2RR), both the reaction current and Faradaic efficiency of the eCO2RR on boron-doped diamond (BDD) electrodes were significantly improved. Here, this effect is referred to as the self-activation of BDD. Generally, the generation of carbon dioxide radical anions (CO2•-) is the most recognized pathway leading to the formation of hydrocarbons and oxygenated products. However, the self-activation process enabled the eCO2RR to take place at a low potential, that is, a low energy, where CO2•- is hardly produced. In this work, we found that unidentate carbonate and carboxylic groups were identified as intermediates during self-activation. Increasing the amount of these intermediates via the self-activation process enhances the performance of eCO2RR. We further evaluated this effect in long-term experiments using a CO2 electrolyzer for formic acid production and found that the electrical-to-chemical energy conversion efficiency reached 50.2% after the BDD self-activation process.
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Hybrid Monte Carlo method with potential scaling for sampling from the canonical multimodal distribution and imitating the relaxation process

Inagaki T., Saito S.

Journal of Chemical Physics （Journal of Chemical Physics） 156 （ 10 ） 2022年03月

ISSN 00219606

　概要を見る

Hybrid methods that combine molecular dynamics methods capable of analyzing dynamics with Monte Carlo (MC) methods that can efficiently treat thermodynamically stable states are valuable for understanding complex chemical processes in which an equilibrium state is reached through many elementary processes. The hybrid MC (HMC) method is one such promising method; however, it often fails to sample configurations properly from the canonical multimodal distribution due to the rugged potential energy surfaces. In this paper, we extend the HMC method to overcome this difficulty. The new method, which is termed potential scaling HMC (PS-HMC), makes use of an artificially modulated trajectory to propose a new configuration. The trajectory is generated from Hamilton's equations, but the potential energy surface is scaled to be gradually flattened and then recovered to the original surface, which facilitates barrier-crossing processes. We apply the PS-HMC method to three kinds of molecular processes: the thermal motion of argon particles, butane isomerization, and an atom transfer chemical reaction. These applications demonstrate that the PS-HMC method is capable of correctly constructing the canonical ensemble with a multimodal distribution. The sampling efficiency and accepted trajectories are examined to clarify the features of the PS-HMC method. Despite the potential scaling, many reactive atom transfer trajectories (elementary processes) pass through the vicinity of the minimum energy path. Furthermore, we demonstrate that the method can properly imitate the relaxation process owing to the inherent configurational continuity. By comparing the PS-HMC method with other relevant methods, we can conclude that the new method is a unique approach for studying both the dynamic and thermodynamic aspects of chemical processes.
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