When we are doing transition state calculations and IRC , we will have the thermodynamic parameters like Gibbs free energy, Enthalpy ,activation energy etc...in a log file. Any suggested references?
As far as I know, it is not possible to obtain rate constants from thermodynamic properties. They depends only on the minimum of the potential surface, while the rate constants depends effectively on the whole shape of the potential.
But your problem is to find the interaction potential, therefore a multidimensional potential surface depending not only on the distance between the interacting particles, but also on the relative orientation and on the internal energy content.
Gaussian allow you to calculate the interaction surface, but practically it is impossible to sample the whole space. Calculating these surfaces is an art.
Even when you have the surface, you need to obtain rates from it and also this is not a simple task. The interaction can happen on more than one surface, and non-adiabatic transitions should also be included.
For some cases, however, some researchers estimate rate coefficients from this kind of data. It is the case of the Forced Harmonic Oscillator (FHO) developed by Igor Adamovich and Sergey Macheret, which, approximating the vibrational ladder with a harmonic oscillator, determined vibration-vibration and vibration-translation relaxation rates, extending the model also to dissociation.
A very popular method to calculate rate coefficients for small molecules is the QCT (Quasi-classical trajectory method). See Esposito for detailed explanation.
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