The theoretical calculation of gas-phase reaction rates

Solving the Schroedinger equation for a sufficient number of geometry configurations we obtain a grid of energy values against the system coordinates, this is the PES. In order to calculate the kinetic constants we need to express the PES in analytic form. Many are the functionals and the models used to fit the energy values. Finally, the calculation of the constant is made by means of the collision trajectories integration (within a classic, semi-classic or quantic scheme) or with the Variational Transition State Theory.