I am performing C-NEB using VASP for barrier energy calculations and I am suggested to calculate vibrational frequency for each states (initial, transition and final). In several research articles I have seen only C-NEB without vibrational frequency calculation. So is it highly necessary to perform vibrational frequency calculations?
Alrik Stegmaier
Thanks for your answer. I agree with what you said; free energies play vital role when the reaction steps have defined intermediates, as in HER/OER, CO2 reduction, etc. However when the reactions are simple like migration of any atom on a surface wouldn't that be enough to know the activation barrier. And I am interested in validation of transition states separately and not including in the reaction itself.
Hi Erakulan,
It is possible for CI-NEB to converge to something that is not a first-order transition state, and to rigorously check this you need to run a vibrational calculation and check for a single imaginary mode along the reaction path. However, not everyone does this check. First, I would suggest you look carefully at all the bond lengths in the transition states you find, and compare the bond lengths and geometry to similar cases where possible (either your own calculations or the literature). At the least, I would perform a vibrational calculation whenever a transition state geometry or calculated barrier looks suspicious or surprising, or when the barrier is really crucial for your scientific argument.
Matt
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