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Maeda S.,Hokkaido University | Taketsugu T.,Hokkaido University | Morokuma K.,Kyoto University | Morokuma K.,Emory University | And 2 more authors.
Bulletin of the Chemical Society of Japan | Year: 2014

This article gives a comprehensive review of the anharmonic downward distortion following (ADDF) method. The ADDF method has been developed as an automated reaction path search method. This method follows the anharmonic downward distortion (ADD) toward transition states and dissociation channels starting from a local minimum on the potential energy surface (PES). Systematic applications of the ADDF method to all local minima provide a global network of reaction pathways on the PES of given chemical formulas. Various extensions have been proposed and applied to many interesting chemical problems such as elucidation of photodissociation mechanisms, structure prediction of H-bonded clusters, mechanistic studies of organometallic catalysis, design of generation-conversion routes of amino acid molecules, and so on. It has also been employed in efficient construction of anharmonic PESs for highly accurate vibrational analysis. These developments and applications are illustrated with some representative results. © 2014 The Chemical Society of Japan. Source


Tokoyama H.,Wakayama University | Yamakado H.,Wakayama University | Ohno K.,Institute for Quantum Chemical Exploration | Ohno K.,Tohoku University
Chemistry Letters | Year: 2016

Polymorphic structures of hexagonal BN (hBN) have been searched by an automated method using quantum chemical calculations based on periodic boundary conditions. Seven hBN structures were explored in an energy range of 2.07 kJ mol-1 at the M06L/6-31G(d) level. Among them, two types of hBN structures were new in comparison with reported hBN, such as Bk and B12 types. © 2016 The Chemical Society of Japan. Source


Maeda S.,Hokkaido University | Taketsugu T.,Hokkaido University | Ohno K.,Tohoku University | Ohno K.,Institute for Quantum Chemical Exploration | Morokuma K.,Kyoto University
Journal of the American Chemical Society | Year: 2015

The photodissociation of small molecules occurs upon irradiation by ultraviolet or visible light, and it is a very important chemical process in Earth's atmosphere, in the atmospheres of other planets, and in interstellar media. Photodissociation is an important method used to thoroughly investigate the fundamental issues of chemical reactivity. Photodissociation involves molecules and reaction fragments moving over ground- and excited-state potential surfaces (PESs). Molecules can move on a single PES (adiabatic pathway) or can cross over from one PES to another (nonadiabatic pathways). For a full theoretical understanding of a photodissociation mechanism, all of the important nonadiabatic and adiabatic pathways must be determined. This is not an easy task. We have developed an efficient computational method, called the global reaction route mapping (GRRM) strategy, that allows a theoretical exploration of ground- and excited-state PESs and their crossing seams in an automatic manner. In this Perspective, we summarize our approaches and present examples of their application together with newly determined chemical insights. These include the complex photodissociation mechanism of the formaldehyde molecule, the exclusive excited-state roaming dynamics of the nitrate radical, and all product channels and conformational memory in the photodissociation of the formic acid molecule. Finally, perspectives for the theoretical design of photofunctional molecules are discussed. © 2015 American Chemical Society. Source


Ohno K.,Tohoku University | Ohno K.,Institute for Quantum Chemical Exploration | Tokoyama H.,Wakayama University | Yamakado H.,Wakayama University
Chemical Physics Letters | Year: 2015

A new carbon family with prism-Cn (n = 3-8, 10, 12, 14, 16, 18, and 20) tube structures has been found by quantum chemical calculations. Periodically and axially piled regular polygons were optimized into the prism-Cn tubes, in which all carbon atoms are equivalent and connected with four single bonds of 0.153-0.161 nm. The relative energies per one carbon atom with respect to graphene are 218-354 kJ mol-1. The lowest energy barriers of tri[4]prismane and tri[6]prismane with similar prism-tube skeletons were found to be ca. 80 kJ mol-1, which gives an expectation that carbon skeletons of the prism-Cn tubes are also stable. © 2015 Elsevier B.V. All rights reserved. Source


Tokoyama H.,Wakayama University | Yamakado H.,Wakayama University | Maeda S.,Hokkaido University | Ohno K.,Institute for Quantum Chemical Exploration | Ohno K.,Tohoku University
Chemistry Letters | Year: 2014

Huge numbers of structures, 7000 isomers and 26229 transition structures, have been searched for C6H6 in quantum chemical calculations by using a GRRM/SCC-DFTB program. The stability of benzene is outstanding. At B3LYP/6-311G(d,p) level, no isomers are found in a wide energy range of 260 kJ mol-1 above the energy of benzene, except for fulvene at 148 kJ mol-1. Other isomers are distributed between 2601250 kJ mol-1. Thirty experimentally known isomers are found in the energy range below ca. 600 kJ mol-1. © 2014 The Chemical Society of Japan. Source

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