Direct Construction of a Dividing Surface of Minimal Flux for   Multi-Degree-of-Freedom Systems: The Equivalence of Conventional and   Variational Transition State Theory
  The fundamental assumption of conventional transition state theory is the existence of a dividing surface having the property that trajectories originating in reactants must cross the surface only once and then proceed to products. Recently it has been shown how to construct a dividing surface in phase space for Hamiltonian systems with an arbitrary (but finite) number of degrees of freedom having the property that trajectories only cross once locally. In this letter we provide an argument showing that the flux across this dividing surface is a minimum with respect to certain types of variations of the dividing surface. In this sense, conventional transition state theory is shown to be equivalent to variational transition state theory. 
H. Waalkens and S. Wiggins