I did a IRC calculation for a molecule having Ge, C, H, N, O and B atoms. At the lower level of theory (hf/3-21g) , its going form reactant to product nicely. But at higher level of theory ( B3LYP/6-31g(d), B3LYP/ 6-311+G(2d,p) , BP86/6-31g(d) and BP86/def2TZVPP) , its going reversed i. e. when the calculation was done for forward direction its going from TS to reactant and vice versa.
Please help me to find out possible cause for this unexpected observations.
Hi Shiv,
I think, it is fine, since the IRC connects TS with both the reactant and the products. The forward/reverse keyword can lead to the reactant/product side depending on the the direction of the imaginary mode of the TS.
regards,
Nijam
Dear Ahmad Alrawashdeh
Multiplicity of molecule is 1
Dear A. Nijamudheen
The IRC calculation connect the TS both side but forward calculations must leads to product. If this is the problem because of direction of imaginary mode, Is there any solution to change it ? or should i try to search other TS, however I have tried several time to search other TS.
Thank You for your suggestion.
Hi Shiv,
I agree with Nijam. Basically, when you run an IRC calculation in forward and reverse directions, you find out the respective minima. The forward calculation often follows the path towards the more deeper minimum i.e towards exothermic direction. This might be reversed in your perception since your description of the reactants and products are based on chemical intution which has nothing to do with the IRC calculatiom. As long as the two minima (obtained after IRC calculation) correspond to your reactant/product, it is fine and you have found the right transition state. Now, you should look at the energies of the minima and decide the exo/endothermic nature of your reaction.
Dear Shubhajit Das
Thank you for your suggestion ..
It might be possible that reaction may endothermic. I will check the energies for both the minima after running the job up to sufficient point. Could I personally email you regarding this calculation by sharing the output file ?
Thank You again
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