Semiclassical theory chemical reaction dynamics

C. Zhu, G. Mil nikov and H. Nakamura, Semiclassical Theory of Nonadia-batic Transition and Tunneling. In Modem Trends in Chemical Reactions Dynamics—Part I., edited by K. P. Liu and X. M. Yang (World Scientific, Singapore, 2003)... 

V. Aquilanti, Resonances in reactions a semiclassical view. The Theory of Chemical Reaction Dynamics, D. C. Clary, ed. Reidel, Dordrecht, 383 413,1986. 

D. G. Truhlar and J. T. Muckerman, Reactive scattering cross sections. Ill Quasiclassical and semiclassical methods, Atom-Molecule Collision Theory (R. B. Bernstein, ed.), Plenum, New York, 1979 L. M. Raff and D. L. Thompson, The classical approach to reactive scattering, Theory of Chemical Reaction Dynamics (M. Baer, ed.), CRC, Boca Raton, FL, 1985. 

This paper also provided much of the early stimulus for developing semiclassical and quantum mechanical theories of chemical reaction dynamics, which is a research field that continues to be active. In addition, this paper provided the foundation for molecular dynamics studies of chemical reactions in condensed phases, including applications to gas-surface scattering and bio-molecular simulation. 

Another direction of research that was fostered by the KPS work was the development of semiclassical theories of chemical reactions. This development arose because the QCT method is an ad hoc procedure for mimicking quantum effects in chemical reaction dynamics wherein quantization is imposed initially and finally but not in-between. In semiclassical methods, one imposes the > 0 limit of quantum mechanics in a consistent way throughout the reactive collision process. The search for a consistent semiclassical theory eventually produced classical S-matrix theory [14], which is a topic of continuing interest in gas-phase dynamics [15], and it also led to the development of Gaussian wave-packet methods for simulating chemical reactions [16]. 

Mark Thachuk joined the UBC Department of Chemistry in 1996. His research program focuses on the study of the dynamics and rates of chemical reactions and processes by mathematical and computational techniques. Typically, such investigations utilize classical, semiclassical, or quantum mechanics, and combine scattering theory with reaction rate and kinetic theories. 

H. Nakamura, Semiclassical approach to charge-transfer processes in ion-molecule collisions, State-Selected and State-to-State Ion-Molecule Reaction Dynamics. Part 2 Theory, Advances in Chemical Physics LXXXII (M. Baer and C. Y. Ng, eds.), Wiley, New York, 1992, p. 243. 

As observed above, both the semiclassical Ehrenfest and PSANB give highly accurate electronic transition probabilities, which are quite close to the full quantum counterparts. In particular, the semiclassical Ehrenfest offers a simpler and convenient computational scheme as far as the electronic transition probability is concerned. Indeed, we have been studying electron current dynamics in chemical reactions with this method. [307] On the other hand, there are situations in which the semiclassical Ehrenfest theory totally fails to reproduce correct dynamics. Even in such a case, PSANB provides not only accurate transition probability but also physically correct view of nuclear motion. We next show such an illustrative example. 

The electronic wavepackets are determined in an expansion with the configuration state functions (CSF) of single and double excitations (CISD) with the STO-6G basis set. This basis set is obviously small, but the main concern in this work is not the accm-acy but qualitative insights about the dynamical electrons in the course of chemical reactions. The program codes for the semiclassical Ehrenfest theory (SET) have been implemented in the GAMESS package [357]. 

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