[Pw_forum] What to do when NEB calculation is difficult to converge?

[Xunlei Ding]

I forgot to give the errors for the last iteration.

     image        energy (eV)        error (eV/A)        frozen

         1     -37090.9593488            0.017636            T
         2     -37090.9338352            0.063849            F
         3     -37090.8813092            0.184154            F
         4     -37090.8113275            0.294601            F
         5     -37090.6869583            0.182737            F
         6     -37090.8612055            0.071489            F
         7     -37091.1264731            0.013874            T

Yours,
Ding

Xunlei Ding wrote:

> Dear all,
> I am now doing a neb calculation on a surface adsorption system with 
> pwscf3.0
> The default values are used in the calculation as below:
>     calculation                   =  neb
>     restart_mode                  =  restart
>     opt_scheme                    =  quick-min
>     num_of_images                 =  7
>     nstep                         =  500
>     first_last_opt                =  F
>     coarse-grained phase-space    =  F
>     use_freezing                  =  F
>     ds                            =  1.0000 a.u.
>     CI_scheme                     =  highest-TS
>     k_max                         =  0.6169 a.u.
>     k_min                         =  0.6169 a.u.
>     path_thr                      =  0.1000 eV / A
>     initial path length           = 12.2601 bohr
>     initial inter-image distance  =  2.0434 bohr
>
> It has more than 400 iterations and has not converged. Should I change 
> some settings, such as ds, or k_max and k_min?
> Below are the activation energies for the last few iterations, and 
> they are not monotone decreasing but oscillating.
> Would anybody give me some suggestions?
>
>     activation energy (->) =   0.273443 eV
>     activation energy (->) =   0.273431 eV
>     activation energy (->) =   0.273719 eV
>     activation energy (->) =   0.273765 eV
>     activation energy (->) =   0.273207 eV
>     activation energy (->) =   0.273148 eV
>     activation energy (->) =   0.273311 eV
>     activation energy (->) =   0.273501 eV
>     activation energy (->) =   0.272957 eV
>     activation energy (->) =   0.272818 eV
>     activation energy (->) =   0.272865 eV
>     activation energy (->) =   0.273155 eV
>     activation energy (->) =   0.272750 eV
>     activation energy (->) =   0.272463 eV
>     activation energy (->) =   0.272443 eV
>     activation energy (->) =   0.272777 eV
>     activation energy (->) =   0.272574 eV
>     activation energy (->) =   0.272118 eV
>     activation energy (->) =   0.272080 eV
>     activation energy (->) =   0.272367 eV
>     activation energy (->) =   0.273228 eV
>     activation energy (->) =   0.272663 eV
>     activation energy (->) =   0.272621 eV
>     activation energy (->) =   0.272935 eV
>     activation energy (->) =   0.273033 eV
>     activation energy (->) =   0.272427 eV
>     activation energy (->) =   0.272386 eV
>     activation energy (->) =   0.272558 eV
>     activation energy (->) =   0.272823 eV
>     activation energy (->) =   0.272391 eV
>
> Yours,
> Ding
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