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

[Ari P Seitsonen]

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