A semiclassical theory in phase space for molecular processes: Formalism based on dynamical characteristic function
Kazuo Takatsuka, Hiroki Nakamura
A new semiclassical theory is formulated by introducing a new distribution function to be propagated in phase space. Primarily this theory is intended to describe molecular collisions such as reactive scattering, but is also applicable to intramolecular processes including bound state problems. This new distribution function is a kind of characteristic function in the terminology of the phase-space-quantum theory developed by Weyl, Wigner, Moyal and others, and is called a dynamical characteristic function (DCF). The equation of motion and some properties of the DCF are presented. The essential feature of our theory is that the semiclassical DCF can be propagated using classical trajectories. This distribution function carried information not only on the density, but also on the phase (action integral). In this sense this theory can be regarded as a kind of phase-space-path-integral formalism. The semiclassical approximation is analyzed from the viewpoint of path integrals. The Wigner distribution function is also discussed in the context of our analysis. As a theoretical application, the semiclassical DCF is shown to reproduce the expression of the periodic orbit theory for bound states. Also, as a simple numerical application, a propagation of the DCF on a nonquadratic (Morse) potential is presented.
The Journal of Chemical Physics•Mar 15, 1985•14 citations