[QE-users] NEB: Atoms do not get relaxed

[Giuseppe Mattioli]

Dear Ari
The NEB is not exactly "stuck"

>      path length          =  8.546 bohr
>      path length          =  9.216 bohr
>      path length          =  9.904 bohr

The MEP length keeps increasing. Maybe a look into the trajectory  
files can tell you what's happening. If any other source of  
misbehavior can be excluded, try to go ahead (maybe fixing the  
position of "useless" atoms). I've experienced NEB in large systems  
converged after several hundreds steps.
HTH
Giuseppe

Quoting Ari P Seitsonen <Ari-Paavo.Seitsonen at cnrs.fr>:

> Dear Users,
>
>   I have a problem in the calculations with the method NEB: The  
> atoms do not get relaxed even if there are clearly forces on the  
> atoms. The electronic structure converges well, and the relaxation  
> of the ions follows nicely when the NEB is not used.
>
>   I have in the input
>
> BEGIN
> BEGIN_PATH_INPUT
> &PATH
>   restart_mode      = 'restart'
>   string_method     = 'neb'
>   nstep_path        =  30
>   ds                = 0.2
>   opt_scheme        = "broyden"
>   num_of_images     = 8
>   k_max             = 0.3
>   k_min             = 0.2
>   CI_scheme         = "auto"
> !  minimum_image     = .true.
>   first_last_opt    = .true.
>   path_thr          = 0.1
> /
> END_PATH_INPUT
>
> and
>
>  &ions
>  /
>
> I have tried with different values of 'num_of_images', 'k_min' and  
> 'k_max', with the climbing image and without. One calculation - a  
> diffusion path of one ad-atom on a surface - worked well, all other  
> become stuck with the output like:
>
>
>      ------------------------------ iteration  12  
> ------------------------------
>
>      cpu =  0   tcpu =   9589.5    self-consistency for image   1
>      cpu =  0   tcpu =   9656.9    self-consistency for image   3
>      cpu =  0   tcpu =   9823.9    self-consistency for image   5
>      cpu =  0   tcpu =  10043.8    self-consistency for image   7
>
>      activation energy (->) =  10.012055 eV
>      activation energy (<-) =   6.833374 eV
>
>      image        energy (eV)        error (eV/A)        frozen
>
>          1     -78491.5920678            0.000987            F
>          2     -78490.3334035            7.018378            F
>          3     -78486.4101831           18.058881            F
>          4     -78481.6171805           29.752151            F
>          5     -78481.5800131           29.996389            F
>          6     -78485.0169815           13.489042            F
>          7     -78487.7020649            7.675245            F
>          8     -78488.4133872            8.072137            F
>
>      climbing image =  5
>
>      path length          =  8.546 bohr
>      inter-image distance =  1.221 bohr
>
>      ------------------------------ iteration  13  
> ------------------------------
>
>      cpu =  0   tcpu =  10165.0    self-consistency for image   1
>      cpu =  0   tcpu =  10267.1    self-consistency for image   3
>      cpu =  0   tcpu =  10487.8    self-consistency for image   5
>      cpu =  0   tcpu =  10710.2    self-consistency for image   7
>
>      activation energy (->) =  10.011390 eV
>      activation energy (<-) =   6.833374 eV
>
>      image        energy (eV)        error (eV/A)        frozen
>
>          1     -78491.5914028            0.000493            F
>          2     -78490.3334036            7.099250            F
>          3     -78486.4101837           17.820470            F
>          4     -78481.6171812           29.761356            F
>          5     -78481.5800130           29.998875            F
>          6     -78485.0169810           13.636010            F
>          7     -78487.7020648            7.675132            F
>          8     -78488.4133870            8.071850            F
>
>      climbing image =  5
>
>      path length          =  9.216 bohr
>      inter-image distance =  1.317 bohr
>
>      ------------------------------ iteration  14  
> ------------------------------
>
>      cpu =  0   tcpu =  10843.3    self-consistency for image   1
>      cpu =  0   tcpu =  10962.6    self-consistency for image   3
>      cpu =  0   tcpu =  11183.6    self-consistency for image   5
>      cpu =  0   tcpu =  11420.4    self-consistency for image   7
>
>      activation energy (->) =  10.011390 eV
>      activation energy (<-) =   6.833374 eV
>
>      image        energy (eV)        error (eV/A)        frozen
>
>          1     -78491.5914032            0.000582            F
>          2     -78490.3334034            7.139704            F
>          3     -78486.4101836           17.548234            F
>          4     -78481.6171812           29.769083            F
>          5     -78481.5800132           29.998295            F
>          6     -78485.0169814           13.849319            F
>          7     -78487.7020642            7.669197            F
>          8     -78488.4133871            8.072137            F
>
>      climbing image =  5
>
>      path length          =  9.904 bohr
>      inter-image distance =  1.415 bohr
>
>      ------------------------------ iteration  15  
> ------------------------------
>
> ...
>
>   So the atoms do not move, the electronic structure is converged in  
> few iterations, but the energies of individual images change in the  
> micro-eVs.
>
>   Any idea would be appreciated; thank you in advance for any hints.
>
>     Greetings,
>
>        apsi
>
> -=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
>   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
>                             Слава Україні



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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I-00015 - Monterotondo Scalo (RM)
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Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>