[QE-users] About CI-NEB job and how to go on after that

[Tom Demeyere]

Hello,

Late answer better than never

NEB calculations can be VERY tricky even for reactions that ‘looks simple’

A popular scheme is to perform a normal NEB to a higher force threshold, say 0.15 eV/Å and then to restart activating the climbing images to something lower like 0.05 eV/Å

If you get two maximas (typically during a dissociation on a slab you also get an additional diffusion which has an energy barrier…) you might want to perform two separate nebs… if you are sure that this is a reasonable path. NEB is known sometimes to produce unreasonably long path, and this could be a reason for this double maxima. You can try playing with the spring constant to remediate this problem

Some more advanced methods claim to fix these issues and improve efficiency such as ‘autoNEB’ (implemented in ASE but not directly in QE) you could also try these…

Good luck

> On 16 Mar 2023, at 20:29, Reinaldo Pis Diez via users <users at lists.quantum-espresso.org> wrote:
>
> CAUTION: This e-mail originated outside the University of Southampton.
>
> Dear folks,
>
> I'm new to NEB calculations.
>
> I'm studying an adsorption-bond breaking/bond formation-desorption process.
>
> From isolated relax jobs (2D lattice kept fixed) using pw.x I've found reasonable 'reactants' and 'products'. Then, I requested a 10-image path that finally converged after a lot a cycles. Initial and final structures were not optimized.
>
> Despite the fact that I've found two maxima in the path, my main question is what to do with that images? Can I trust them or do I have to optimize them to confirm that they are critical points on the potential surface of the system?
>
> Also, do I have to do a sort of convergence test by increasing the number of images to confirm that the path does not change?
>
> Finally, any hint about NEB calculations and/or any pointer to a sort of tutorial on how to be successful on such jobs is very welcome.
>
> Best regards,
>
> ---
> Reinaldo Pis Diez
> PhD in Chemistry
> Principal Researcher - CONICET (Argentina)
> Full Professor - UNLP (Argentina)
> Email: pis_diez.at.quimica.unlp.edu.ar
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