[Wien] mini

[celhin]

Dear Kakha and Wien2K users,

It also happened to me. Apparently the convergence was also achieved after 14
scf cycles with the output "ec cc and fc_conv 1 1 1", but the program did not
stop and began to recalculate again from cycle 1 and then stop after 12 cycles
with the output "ec cc and fc_conv 1 1 1".

Best,
Céline.


Kakhaber Jandieri <Kakhaber.Jandieri at physik.uni-marburg.de> a écrit :

> Dear Wien2K users,
>
> As I wrote in my previous letters, I am trying to minimize the atom
> positions in GaP supercell where one of the P atoms is replaced by N-N
> interstitial molecule.
> I found some strange (in my opinion) behaviour of  "mini".
> Apparently the convergence was achieved after 18 scf cycles with the
> output "ec cc and fc_conv 1 1 1". The  distance  between  relaxed  N-N
> atoms was 1.57 A.
> But the program did not stop and began to recalculate again from cycle 1.
> After 16 scf cycles the situation was repeated but now  the  distance
> between  relaxed  N atoms was reduced down to  1.27 A.
> And so on without ending.
> In my opinion even 1.27 A  is already too small value (this is almost
> the interatomic distance in isolated N2 molecule), but it was
> decreasing  further and further.
> So, finally I had the problems with overlapping spheres in spite of very
> small  RMT(N)=1.1 bohr.
>
> In output file of our cluster I found the following (below some fragment
> of this file is shown):
>
> ..............................................................
> ..............................................................
> in cycle 18    ETEST: .0001117900000000   CTEST: -.0009873
> ec cc and fc_conv 1 1 1
>
>>   stop
> Fallback to compatibility mode with "old" save_lapw
> broyden files deleted, clm*, dmat*, vorb*, vresp*, eece*, scf and struct
> files saved under GaPNN_1
> 20.841u 0.352s 0:21.70 97.6%    0+0k 0+20648io 0pf+0w
> 0.844u 0.276s 0:01.54 72.0%    0+0k 1272+16896io 8pf+0w
> clmextrapol_lapw has generated a new GaPNN.clmsum
> ec cc and fc_conv 0 0 0
> in cycle 2    ETEST: 0   CTEST: 0
> ec cc and fc_conv 0 0 0
> in cycle 3    ETEST: 0   CTEST: 0
> ec cc and fc_conv 0 0 0
> .............................................................
> .............................................................
>
>
> In my opinion 1.57 A  is much reasonable value for relaxed N-N distance
> then 1.27 A or even smaller value.
> I still wonder why the program begins recalculation after the apparently
> successful message: "ec cc and fc_conv 1 1 1"?
>
> Is there some possibility that the reason is the specific position of
> N-N interstitial pair?  In my initial structure file  P(0,0,0) atom was
> replaced by N-N interstitial pair having the positions symmetrically
> shifted from (0,0,0) along  the z-direction. The constrains (0.0, 0.0,
> 1.0) in my case.inM   file  allow the displacement of N atoms only along
> the z-direction. My native thought was that may be (0,0,0) is some
> specific position in the supercell. If I know correctly, in usual
> minimization tasks with substitution impurity, the atom at (0,0,0)
> position should have full constrains in all directions. I tried to
> replace  other P atom in the middle of initial 2x2x2 supercell, but "x
> sgroup" always returns the converted supercell where N-N pair is near
> (0,0,0), (0.5,0.5,0.5), (0,0,0.5)  and so on   positions.
>
>
> I will be extremely thankful for any suggestion.
> Kakha
>
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