||Yuuichi Orimoto, Yuriko Aoki, and Akira Imamura, Extraction of One-Handed Helical Frontier Orbital in Even [n]Cumulenes by Breaking Mirror Images of Right- and Left-Handed Helical Orbitals: Theoretical Study, J. Phys. Chem. C, 123, 11134-11139, 2019.04.
||Yuuichi Orimoto, Kosuke Ishimoto, Yuriko Aoki, Role of Pyridinium Groups and Iodide Ions in Photoelectrochromism in Viologen-Based Ion-Pair Charge-Transfer Complexes
Molecular Orbital Analysis, Journal of Physical Chemistry C, 10.1021/acs.jpcc.7b10281, 122, 8, 4546-4556, 2018.03, Quantum chemistry calculations were performed to examine the fundamentals of photoinduced electron transfer (ET) in viologen (V)-based ion-pair charge-transfer complexes and the resulting photoelectrochromism with respect to photoswitching applications. For the purpose, the photoinduced ET from counter anions to viologen or biphenyl (BP) derivatives was modeled, and its relationship with their structures was analyzed. Our results showed that the electron reduction of V2+, assuming photoinduced ET, that is, V2+ → V+ → V0, changes the conformational preference from a twisted to a planar structure because of the lowest unoccupied molecular orbital (LUMO) in V2+ showing a planar tendency. A similar feature appears in the reduction of neutral BP, that is, BP0 → BP- → BP2-, leading to a twisted → planar preference change because of the LUMO in BP0. The similarity between V2+ and BP0 can be explained by their similar MO shape and their identical number of electrons. The time-dependent density functional theory (TD-DFT) was applied to predict the absorption spectra of viologen and BP derivatives with iodide ions considered as counter anions. In addition, geometrical optimization using the TD-DFT method was performed for viologen derivatives to stabilize a specific excitation to simulate laser irradiation. Our simulation implies that laser absorption can cause a twisted → planar change accompanied by a weak charge transfer if we ignore the time scale. Moreover, it was found that the iodide ion is necessary for near-infrared (NIR) absorption corresponding to the telecommunication wavelength. This is because NIR absorption is attributed to a narrow energy gap generated by the insertion of orbital levels of iodide ions into the original energy gap of viologen. Contrary to the above-mentioned similarity, BP was found to show totally different features from viologen regarding (1) the magnitude of the polarization between the molecule and counter anions, (2) the laser-induced excitation behavior, and (3) the peak position of NIR absorption. From the MO analysis, the role of pyridinium groups, which cannot be replaced by phenyl groups, was theoretically explained..
||Yuuichi Orimoto, Kohei Kato, Yuriko Aoki, Importance of Through-Space Interaction of [2,2′]-Paracyclophane-oligo(p-phenylenevinylene) Molecular Wires for Photovoltaic Application and Effective Wire Design by Chemical Substitution, Journal of Physical Chemistry C, 121, 33, 17703-17711, 2017.08.
||Yuuichi Orimoto, Kohei Otsuka, Kazuma Yagyu, Hiroshi Tochihara, Takayuki Suzuki, Yuriko Aoki, Theoretical Study of Cu Intercalation through a Defect in Zero-Layer Graphene on SiC Surface, Journal of Physical Chemistry C, 10.1021/acs.jpcc.7b00314, 121, 13, 7294-7302, 2017.04.
||Yuuichi Orimoto, Yuriko Aoki, Automated property optimization via ab initio O(N) elongation method
Application to (hyper-)polarizability in DNA, Journal of Chemical Physics, 10.1063/1.4956456, 145, 2, 2016.07, An automated property optimization method was developed based on the ab initio O(N) elongation (ELG) method and applied to the optimization of nonlinear optical (NLO) properties in DNA as a first test. The ELG method mimics a polymerization reaction on a computer, and the reaction terminal of a starting cluster is attacked by monomers sequentially to elongate the electronic structure of the system by solving in each step a limited space including the terminal (localized molecular orbitals at the terminal) and monomer. The ELG-finite field (ELG-FF) method for calculating (hyper-)polarizabilities was used as the engine program of the optimization method, and it was found to show linear scaling efficiency while maintaining high computational accuracy for a random sequenced DNA model. Furthermore, the self-consistent field convergence was significantly improved by using the ELG-FF method compared with a conventional method, and it can lead to more feasible NLO property values in the FF treatment. The automated optimization method successfully chose an appropriate base pair from four base pairs (A, T, G, and C) for each elongation step according to an evaluation function. From test optimizations for the first order hyper-polarizability (β) in DNA, a substantial difference was observed depending on optimization conditions between "choose-maximum" (choose a base pair giving the maximum β for each step) and "choose-minimum" (choose a base pair giving the minimum β). In contrast, there was an ambiguous difference between these conditions for optimizing the second order hyper-polarizability (γ) because of the small absolute value of γ and the limitation of numerical differential calculations in the FF method. It can be concluded that the ab initio level property optimization method introduced here can be an effective step towards an advanced computer aided material design method as long as the numerical limitation of the FF method is taken into account..
||Yuuichi Orimoto, Yuriko Aoki, Computational Study of Cu–Containing Artificial DNA
Twist Angle Dependence of Magnetism, ChemistrySelect, 10.1002/slct.201600940, 1, 17, 5521-5529, 2016.01.
||Yuuichi Orimoto, Kai Liu, Yuriko Aoki, Elongation method for electronic structure calculations of random DNA sequences, Journal of Computational Chemistry, 10.1002/jcc.24047, 36, 28, 2103-2113, 2015.10, We applied ab initio order-N elongation (ELG) method to calculate electronic structures of various deoxyribonucleic acid (DNA) models. We aim to test potential application of the method for building a database of DNA electronic structures. The ELG method mimics polymerization reactions on a computer and meets the requirements for linear scaling computational efficiency and high accuracy, even for huge systems. As a benchmark test, we applied the method for calculations of various types of random sequenced A- and B-type DNA models with and without counterions. In each case, the ELG method maintained high accuracy with small errors in energy on the order of 10
hartree/atom compared with conventional calculations. We demonstrate that the ELG method can provide valuable information such as stabilization energies and local densities of states for each DNA sequence. In addition, we discuss the "restarting" feature of the ELG method for constructing a database that exhaustively covers DNA species..