Calculating reaction kinetics
Reaction kinetics are described in terms of reaction rate coefficients. The rate coefficients are evaluated in the transition state theory framework using information about the energies, geometries, and vibrational frequencies of reactants, products, and transition state. In order to achieve better agreement with experiment it might be advantageous to increase the reaction threshold value from the DFT calculated one and to scale calculated harmonic frequencies to account for DFT deficiency and for anharmonic effects.
The threshold correction can be applied either on a basis of more accurate ab initio calculations or based on the comparison of calculated and experimental rate coefficients. It appears that a value in the region of 6-7 kcal/mol describes DFT error adequately.
The recommended correction factors for DFT frequencies can be found at the NIST website for a variety of exchange-correlation functionals.
To calculate reaction kinetics
- Choose Modules | CASTEP | Analysis from the Materials Studio menu bar.
- Select Reaction kinetics from the list of properties.
- Ensure that the desired 3D Atomistic collection document (
seedname.xod) is the currently active document. - Specify the temperature range of interest.
- Check the Apply tunneling correction checkbox if the reaction involves motion of light elements.
- Optionally specify a Threshold correction and a Vibrational frequencies scaling factor.
- Click the Calculate button.
- A new study table document,
seedname.std, is created in the results folder.
See Also:
Reaction kinetics theory
Analyzing CASTEP results
Updating structure
CASTEP Analysis dialog