Generalized Transition State Theory
Any form of TST, such as microcanonical variational TST, canonical variational TST, and improved canonical variational TST, in which the transition state is not necessarily located at the saddle point, is referred to as generalized transition state theory.
Microcanonical Variational TST
A development of transition state theory in which the dividing surface is varied so as to minimize the rate calculated for a fixed energy. The rate expressions obtained in a microcanonical treatment can be integrated over the energy, taking into account the statistical distribution over energy states, so as to give the canonical, or thermal rates.
Canonical Variational TST
A development of transition state theory in which the position of the dividing surface is varied so as to minimize the rate constant at a given temperature.
Improved Canonical Variational TST
A modification of canonical variational transition state theory in which, for energies below the threshold energy, the position of the dividing surface is taken to be that of the microcanonical threshold energy. This forces the contributions to rate constants to be zero if they are below the threshold energy. A compromise dividing surface is then chosen so as to minimize the contributions to the rate constant made by reactants having higher energies.
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