Hello everyone,
I am new in this topic and I am trying to reduce the reaction steps involved in oxidation of carbon in a fuel cell with the help of Ansys Chemkin pro (also any other possible ways may be suggested). However, Chemkin pro requires the reactions with the kinetic and thermodynamic parameters such as activation energy, pre exponential factor... How can i calculate these parameters? I couldn't find any database for my reactions especially for surface kinetics.
I have many reactions, however i am adding here a small section of it, so that maybe anyone could explain for these reaction chain the steps and for the rest i will follow the same process.
One possible way of oxidation is here:
C(s) + H2O (C-OH)ads + H+ +e-
(C-OH)ads (CO)ads + H+ + e-
(C-OH)ads + H2O -> C(s) + CO2(g) + 3H+ + 3e-
I did some research and i found out that, firstly it is required to do vibrational frequency calculation and further the parameters can be calculated through DFT. If it comes to the case that i need to do vibrational frequency calculation, i found out that PSI4 is a free software for it. However, it needs input file of the molecules in cartesian co-ordinates. How do i find these geometrical properties for the molecules in my reactions. Are there any database for it?
I am open for any possible solutions as long as the software is available for free (for Ansys i have the license). Can anyone guide me on how can i do the calculations that i am seeking for?
I thank you in advance.
Regards,
Sachin Hegde
For starting structures you can dig through the Cambridge crystallographic database: https://www.ccdc.cam.ac.uk/
Please be aware: a DFT structure optimization creates nonsystematic deviations from real geometries, so the interatomic distances may shrink or enlarge depending on the functional and basis set you choose.
When it comes to your adsorption geometries, you will have to draw yourself whatever you consider the proper candidate structures and be prepared to draw multiple starters. Especially for the transition states, multiple candidates will have to be tried.
When you have optimized structures for all educts, products and transition states, you can run the frequency calculations which is also a verification that they are actually what you need: a minimum (educt/product) should have no imaginary frequency and a transition state exactly one (first order saddle point).
This data can be fed into a calculation tool for kinetic parameters, whatever method is preferred in your community.
Caveat: there will be a somewhat systematic difference between the kinetic parameters from calculations (depending on the methods you used) and kinetic parameters from experiments. Therefore you cannot simply mix these in model calculations. In the best case, there are close-to-systematic factors which can be used to account for the difference, but usually that is not the case and I would expect that for you. For that reason, absolute rates may differ strongly from reality, but the relative contributions can be assessed quite well.
Jürgen Weippert , Thank you very much for the information.
Could you also kindly suggest some of the free toolsets for modeling, DFT analysis and for kinetic parameter extraction for m application?
i found out Quantum espresso is free for DFT analysis
Which is a good modeling software that is free?
Also the calculation tool for kinetic and thermodynamic parameter estimation?
Among the free tools for DFT, Quantum Espresso seems to be the most popular, but I never used it and so I don't know what's the most convenient structure editor for it, but there seem to be plenty of Youtube tutorials on it. Since I got my education from KIT, I was primarily trained on Turbomole which is mainly being developed there, but of course that costs money. For surface related calculations, VASP seemed to be the most used software when I attended conferences, but that costs even more.
My last calculation of kinetic parameters was also quite a while ago (and only on molecular level), back then I used Multiwell https://multiwell.engin.umich.edu/about/
I don't know if that works with Quantum Espresso output files, though, you'll have to check the description.
- Badges
- Science topic