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How to get the reaction rate?
Posted: Wed Mar 21, 2007 4:12 am
by hlzya
Hi
After I use the method such as NEB and dimer, I can obtain the activation energy and prefactor. I want to konw how I can get the reaction rate at certain temperature using the above mentioned information.
Thanks!
Posted: Wed Mar 21, 2007 7:32 am
by graeme
The harmonic rate is R=v exp(-dE/kT) where dE is the activation energy and v is the prefactor.
Posted: Tue Apr 10, 2007 7:05 am
by lanjh
But how to calculate the prefactor?
Calculating the harmonic prefactor.
Posted: Tue Apr 10, 2007 5:12 pm
by dano
The harmonic prefactor looks like this:
v = Prod (vmin_i) /Prod (vsaddle_j)
where (vmin) is the normal modes at the minimum and i goes from i=1->3N
and (vsaddle) is the normal modes at the saddle and j goes from j=1->3N-1
The one imaginary mode at the saddle is not left out of the product
N is the number of degrees of freedom (ie. atoms that are not frozen)
Posted: Wed Apr 11, 2007 12:56 am
by lanjh
thanks, Sir!
I am still not very clear about what your reply. Do you mean that vmin_i and vsaddle_j are the normal modes of reactant and saddle? vmin_j denotes
one normal mode or more?
Furthermore, Prod represents what ?
I am eager to your reply, thanks very much!
Posted: Wed Apr 11, 2007 1:48 am
by graeme
These questions are a little basic for this forum. A short description of harmonic transition state theory can be found in the following class notes:
http://theory.cm.utexas.edu/statmech/notes/notes12.pdf
The equation that Dan gave you is 12.13 in these notes, and the text (along with any statistical mechanics textbook), describes the harmonic approximation.