Hey all,
I am a beginner for Gaussian package. I am little bit confused between QST2 and IRC calculations implemented in Gaussian package. IRC is done for calculating reaction paths but as far as I understand QST2 also gives the transition state which we need while calculating reaction paths. Please help me in understanding these two different/same things..
Thank you.
In short, QST2 is a method to obtain the structure of the transition state, whereas IRC or Intrinsic Reaction Coordinate is the method to validate whether your calculated TS (obtained via QST2 or QST3) is correct or not. IRC connects the calculated TS with reactant(s) on one side and product(s) on the other. By checking their (reactant(s) and product(s)) structure one can confirm whether the calculated TS is the desired one or not.
But In case of QST3 also, we have to give initial guess for the TS structure. How we guess TS because there can be many possibilities? Isn't it some kind of TS confirmation?
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