SOUMEN

Dear Struanr; Thank you very much for your reply and guidance. I am glad to say after considering hindered rotors treatment for R1, R2, Add-I, Add-II, Add-III, TS-2, and TS-3 we have been able to get rid of most of the negative frequencies. There are only two (or we can say one) negative rate coefficients so far. One is R1 (deficient reactant) to ADD-I (association product) , and the other one is the reverse of it i.e., ADD-I to R1. We can very easily neglect the second one as it is of the order...

Dear Struan; Thank you very much for reply and guidance. I am glad to say after considering hindered rotors treatment for R1, Add-I, Add-II, Add-III, TS-2 and TS-3 we have able to get rid of most of the negative frequencies.

Thank you for your time and effort to clarify all my doubts. I believe we are at the end of this conversation trail. So far I have learned a lot from our conversation. I have my last queries regarding the PES we have been talking about so far. The file "File1_withT" contains the full PES for your reference. In the PES Add-I, Add-II and Add-III are rotational isomers. A COOH group rotates about an angle slightly larger than 180° ( dihedrally) via TS-2 and TS-3. we already discussed output of this...

Thank you very much for your reply. So, you were correct. I somehow put a wrong value of imaginary frequency for TS-5. The actual value of it is around 1006.17 cm-1. That solves the issue with tunneling. Now to solve the issue with negative rate coefficients your suggestion is to treat intermediate species having low barriers as a single one and combine their states. I want your guide here. If I understood correctly one possible option is to remove Add-II and Add-III and directly connect Add-I with...

Thank you very much for your reply. Here I am attaching two files. Both are usually the same. One of them has Eckart tunneling in on (File1_withT) and in the other one Eckart is off (File2_withoutT). The system is like the Query 1. All the barriers are significantly below the isolated reactant energy. Also, there is a branching of products. From the output, it can be observed when tunneling was considered one of the branches getting zero Bartis-Widom phenomenological rate constants. Whereas when...

Query 1: A multi-well reaction that we are currently studying has all its transition states below the isolated reactant. The highest barrier lies below 17 kcal/mol from the isolated reactant and the rest are around ~ 50 kcal/mol below the isolated reactant energy. In that reaction, while dealing with intermediate uni-molecular step we are using Eckart tunneling with RRKM technique. We face difficulties like Chemically significant eigenvalues (CSE) not well separated from internal energy relaxation...

Dear struanr ; Thank you very much. This seems to solve my problem.