My Community

Hi dear all,

Because I m really new to VASP and its theory, I have a (maybe basic) question.

I did a NEB calculation, however, as I know it s just for 0K. SO how can I extend that to other temperatures?

Thanks
Kambiz

I've heard the NEB described as a 0K method before, but this is not an accurate characterization. The NEB is used to calculate energy barriers for a reaction so that the rate can be evaluated within the harmonic approximation to transition state theory (HTST). This rate is of the Arrhenius form, [rate = nu exp(-dE/kT)]. Classically, the rate of a reaction goes to zero at 0K. HTST is accurate at low temperature and will deviate when the thermally accessible regions around the minimum and saddle are poorly approximated by a harmonic expansion of the potential around these critical points. This temperature will be system dependent - generally higher for solids and lower for soft matter. Above this temperature, when the harmonic approximation does not hold, sampling methods can be used quantify reaction rates. These include forward flux sampling, path sampling, mile-stoning, transition interface sampling, variational TST, and dynamical corrections to TST, among others. These methods are also, particularly with DFT, so computationally expensive that even though it's possible, few people actually calculate rates with them.