XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Exploring Multiple Potential Energy Surfaces
Satoshi Maeda,1,2 Koichi Ohno3 and Keiji Morokuma2,4
1The Hakubi Center, Kyoto University, Kyoto 606-8302, JAPAN
2Fukui Institute for Fundamental Chemistry, Kyoto University, Kyoto 606-8103, JAPAN
3Toyota Physical and Chemical Research Institute, Nagakute, Aichi 480-1192, JAPAN
4Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, GA 30322, USA
Nonadiabatic transitions play key roles in many chemical reactions [1], including photoreactions, ion-molecule reactions, spin-flip reactions, and so on. Since multiple potential energy surfaces (PESs) are involved in such reactions, one has to explore multiple PESs systematically to uncover its entire reaction mechanism. Minimum on seam of crossing (MSX) structures are often considered as critical points of nonadiabatic transitions. On each PES, chemical bond rearrangements may take place via a transition state (TS) structure. In short, one has to locate all important MSXs as well as TSs for multiple PESs.
On excited state PESs, molecules take unexpected (chemically unstable) geometries more frequently than on the ground state PES. Hence, use of an automated reaction path search method is highly recommended to locate all important TSs and MSXs systematically. However, automated exploration of excited state PESs has been very difficult because there are singular points in low energy regions of excited state PESs due to conical intersections (CIs). There has been no practical method for the automated MSX search either.
Recently, we have proposed a recipe for exploring multiple PESs by using an automated reaction path search method which has previously been applied to single PESs [2]. Although any such methods can be used in the recipe, the global reaction route mapping (GRRM) method was employed in this study [3]. By combining GRRM with the proposed recipe, all critical regions, i.e., TSs, CIs, MSXs, associated with multiple PESs can be explored automatically. In applications to photodissociation reactions of simple molecules, the present approach led to discovery of many unexpected nonadiabatic pathways, by which some complicated experimental data have been explained very clearly [4].

[1] S. Nanbu, T. Ishida, and H. Nakamura, Chem. Sci. 2010, 1, 663.
[2] S. Maeda, K. Ohno, and K. Morokuma, J. Phys. Chem. A 2009, 113, 1704.; S. Maeda, K. Ohno, and K. Morokuma, Adv. Phys. Chem. Submitted.
[3] K. Ohno and S. Maeda, Phys. Scr. 2008, 78, 058122.
[4] S. Maeda, K. Ohno, and K. Morokuma, J. Phys. Chem. Lett. 2011, 1, 1841.; R. Nádasdi, G. L. Zügner, M. Farkas, S. Dőbé, S. Maeda, and K. Morokuma, ChemPhysChem 2010, 11, 3883.; H. Xiao, S. Maeda, and K. Morokuma, J. Phys. Chem. Lett. 2011, 2, 934.


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