XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Oral presentations only. Posters only. Show all.

Efficient Performance of the GRRM Method as an Explorer of Novel Reaction Channels and Chemical Structures.
Koichi OHNO1 and Yuto Osada2
1Toyota Physical & Chemical Research Institute, Japan

2Department of Chemistry, Graduate School of Sciencre, Tohoku University, Japan
It has been believed to be impossible to search all of equilibrium structures (EQ) and transition structures (TS) by automated procedures based on quantum chemical calculations, if the number of atoms exceeds four atoms [1]. However, the global reaction route mapping (GRRM) method based on the anharmonic downward distortion (ADD) following reaction pathways made it possible to explore the entire reaction channels as well as the whole EQ and TS [2]. Although it has been claimed that a stochastic approach with repeated uses of geometrical optimization enable us mindlessly to find all chemical structures for a given chemical formula such as BCNOS [3], much more structures have been discovered by the GRRM method [4].
In this work we will demonstrate how the GRRM method [2] efficiently discovers EQs and TSs, when some parameters are varied to reduce computational demands. For limited ADD following only tracing large ADD (l-ADDf), ratios of the computation time, the explored number of EQ and that of TS with respect to the full ADD following (f-ADDf) were systematically studied. When l-ADDf treatments are combined with stochastic generation of starting structures, more than 80 % of EQ and 50 % of TS could be efficiently explored in one tenth of computation time with respect to that for the f-ADDf. This tendency of l-ADDf indicates promising performance of the GRRM method in its application to larger systems for finding unknown reaction pathways and new isomers.

[1] F. Jensen, Introduction to Computational Chemistry, First Ed., Wiley (1999).
[2] K. Ohno, S. Maeda, Chem. Phys. Lett. 384, 277 (2004); S. Maeda, K. Ohno, J. Phys. Chem. A 109, 5742 (2005); K. Ohno, S. Maeda, J. Phys. Chem. A 110, 8933 (2006).
[3] P. P. Bera, K. W. Sattelmeyer, M. Saunders, H. F. Schaefer III, P. v. R. Schleyer, J. Phys. Chem. A, 110, 4287 (2006).
[4] K. Ohno and Y. Osada, to be published.


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