My purpose is to simulate Chemical reaction using Computational simulation tool (DFT tool) for aquiring transition state, activation energy, reaction rate depending on Temperature and Pressure.
I want to simulate Chemical reactions in Si epitaxy(CVD).
I need to get reaction path, energies and reaction rate(Arrhenius equation) depending on Temperature and Pressure.
So I need DFT tools that can calculate transition states shape and energy of solid(wafer or contamination particles)-gas(precursor) reactions and gas-gas reactions depending on Temperautre and Pressure.
I looked into VASP, and I heard that energy and thermodynamic calculations in transition state are possible, but pressure cannot be considered, only in the condensed system (solid and liquid) and gas phase reaction is not possible.
So I looked at the Gaussian, but I didn't know exactly if it was possible to calculate transition state.
I want to know what DFT tool is best for my case.
Also, I wonder how we can calculate the pre-exponential factor and alpha value in Arrhenius equation even if we know the structure and activation energy of the transition state.
k=ATαexp(-Ea/RT)
This is only a partial answer, but Gaussian can find transition states. Look at opt=ts, opt=qst2, and opt=qst3 in the manual (which is available online without requiring to be a Gaussian user). You can use DFT for this, but remember that DFT is a general term with dozens of specific density functionals available, and making a good choice of which density functional to use for your project can be difficult.
You may have to combine multiple tools here. The DFT software calculates the geometry and the vibrational frequencies from which you can calculate rate coefficients on a TST level quite easily.
Regarding the pressure dependence: for a standard bimolecular reaction the rate is just the coefficient times the pressures or concentrations, but if you talk about Lindemann-mechanism, RRKM or master equation calculations you will need an additional tool like Multiwell:
https://multiwell.engin.umich.edu/about/
It has also tools to "talk" directly with Gaussian.
Well, you should use Nudged elastic band methodology if you know the initial and final state of your reaction for use this methodology you will know the reagents and products. Otherwise if you know the reagentes but unknown the products you will should calculate a PES that give you this information. Molecular dynamic abnitio also could use for this.
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