Analysis of Chemical Reaction on Adiabatic Potential Energy Surface from a Viewpoint of Anharmonicity and Orbital Mixing : Bifurcation of Anharmonic Downward Distortion Following Paths and Natural Reaction Orbitals

概要

bifurcation of ADD stationary paths around a potential minimum is studied in detail
(Chapter 2).
The second topic is the automation of orbital analysis along IRC. As noted above,
reaction pathway search has been automated to a considerable extent. [26,104,105,113]
This automation drastically increased the amount of data provided by the reaction
pathway search calculation. The manual analysis in a conventional manner is apparently unsuitable for such a great amount of data anymore. Thus, a new automated
analysis method compatible with the automated reaction pathway search is needed.
Among the various reaction mechanism analyses, molecular orbital analysis seems to
be one of the most basic and essential analyses because it can clarify the driving force
of the reaction. [54, 55]. Automated extraction of important MO is not only convenient
but also technically important for the application of data science to computational
chemistry. [120, 173] Since data scientific approaches require a large amount of data,
automation of data sampling is so essential. Combined with the aformentioned technique of automated reaction pathway search, [104] an automated method to extract
essential MOs for the reactivity is expected to be a powerful tool for the realization of
an automated data sampling system with computational chemistry.
Although there are various sophisticated orbital analysis methods, [35–37,44,48–51,
68, 103, 112, 117, 121, 124, 131, 144, 145] there seems to be no method designed for the
automated extraction of MOs responsible for given reaction process. Accordingly, new
orbital analysis method specialized to the automated extraction needs to be developed.
For the design of such new orbital, the idea of ADD gives a big hint. As shown in [150],
for example, ADD or relaxation of potential energy is induced by the configuration mixing induced by nuclear displacements. Actually, the configuration mixing induced by
nuclear displacements can be represented with orbital basis. This is essentially because
differential operators with respect to nuclear coordinates act as if they are one-electron
operators. Even though some additional consideration is required for multiconfigurational theory, the configuration mixing in such cases can also be represented with MO
basis. This implies that there exits a definition of MO which optimally characterizes the
essential configuration mixing for the increase of ADD. Considering that the increase of
ADD is necessary for a direction to be that of reaction, MO responsible for the increase
of ADD seems to be essential for the reaction. That is, the driving force of a chemical
reaction is expected to be extracted with such MO.
It should be referred that intrinsic soft molecular orbital (ISMO), a technique to
extract MOs characterizing the response to partial charge fluctuation, was proposed
by A. Morita and S. Kato. ...

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