Firefly and PC GAMESS-related discussion club



Learn how to ask questions correctly


Re^2: catalysis, negative energy activation in MP2 calculation

sanya
sanya@photonics.ru


The structure in your output is a transition state because it has exactly one imaginary frequency. Moreover, it is this frequency that is expected to be the reaction coordinate in this type of reactions. Therefore, it is the correct transition state.

As for the energies... Can you give me the MP2 energies of each reactant, catalyst, and product? The energy of the transition state is already in your output.

When you calculate the energy of a process (Initial state -> Final state), its energy is E(Final state) - E(Initial state). For the processes in my previous post, the initial state is X + Y + C (the energy is E(X)+E(Y)+E(C)), the final state is XYC* (its energy is E(saddle point)). The difference E(saddle point) - (E(X)+E(Y)+E(C)) is the activation energy, and if everything is correct, it is positive. As for the products, you don't need them for the calculation of the activation energy, you only may compare the transition state energy with the energy of the products E(Z)+E(C) to make sure that the transition state is higher in energy than the products. Of course, all the energies should be obtained by the same method, say, RHF or MP2.

On Tue Feb 23 '10 4:33pm, Ronald Conol wrote
--------------------------------------------
>Thank you for your explanation and I understand it !. I have another problem and i Hope you can still help me with it. I found out that what I've obtained is not really the transition state itself but rather it could be  an intermediate of the reaction because its energy with respect to the transition state as well as the reactant is at the minimun and it has a single imaginary frequency ( you can look at my output attached). Now is there any technique that I can used to push this structure uphill to obtain the Transition structure?


[ Previous ] [ Next ] [ Index ]           Wed Feb 24 '10 3:34am
[ Reply ] [ Edit ] [ Delete ]           This message read 649 times