Can the NEB method be used for a non-elementary reaction?

[mbrumovsky]

Dear all,

I am wondering whether it is appropriate to use the NEB method for finding transition state(s) in reactions that may not necessarily be elementary, such as beta-elimination of halogen atoms in halogenated hydrocarbons on a solid catalyst. These reactions are sometimes thought of as elementary because no reaction intermediates have been detected, but may actually occur by stepwise cleavage of two neighbouring C-X bonds. If a beta-elimination is run with NEB, is the method capable of correctly identifying whether the reaction is elementary or stepwise?

Thank you very much in advance,
All the best
Miroslav

[graeme]

Hi Miroslav,
Yes, the NEB can determine if a reaction path is stepwise or concerted. If it does occur in two steps, you should see an intermediate minimum in the minimum energy pathway. It is usually most efficient to minimize that structure and calculate the two steps separately with the NEB, but you don't have to do that.

[mbrumovsky]

Dear Prof. Henkelman,

Thank you for the clarification! I suppose that if two steps are apparent in the NEB calculation, it would be also more accurate to divide it into two separate calculations as you've suggested because the LCLIMB functionality works only for the highest TS.

All the best
Miroslav

[graeme]

Exactly - then you get both saddles accurately with the climbing image.

[mbrumovsky]

Good, thank you Prof. Henkelman for your support. Have a nice day!