[Wien] WARNING : Please restart anew from final position

[Kakhaber Jandieri]

Dear Laurence,

Thank you very much.

Unfortunately, after some iteration step  I missed the warnings :
WARNING: Step size reduced due to overlapping spheres
and
WARNING: CURVATURE CONDITION FAILED

According to your tutorial, the last one means that the forces and  
energy are not consistent and one of the possible reasons can be the  
small RKMAX. I guess that in my case the reason is different since I  
see the same warning for increased value (7 instead of 5) of RKMAX.  
May be the reason is given in the first warning about the overlapping  
spheres. Below I will try to justify my suggestion.

I am trying to relax the GaAs slab containing two substitutional  
nitrogen atoms in surface  layer. I constructed the supercell  
containing 72 non-equivalent atoms: 5 layers with 12 atoms in each,  
appr. 10 Angstr. Vacuum and the passivation  layer of hydrogen atoms.  
I fixed only the hydrogen layer and the first GaAs layer. I remember  
your letter where you had some doubts about such consideration, but I  
want to compare the simulated Scanning Tunneling Microscopy images  
with that obtained in Phys. Rev. B75, 035338 (2008), where the similar  
approach was used (fixed layer, pasivation by hydrogen). So on current  
stage I decided to stay in frames of this approach.

I have the following values of RMT:
RMT(Ga)=2, RMT(N)=1.68, RMT(H)=1.3

I think that RMT(N)=1.68 is the reason for my problems. The supercell  
was relaxed correctly up to some iteration step. Then the Ga and N  
spheres began to touch each other and the problems appeared. I have  
the following ground for such suggestion. The Ga-N distance in my  
“partially relaxed” supercell is 1.95 Angstr. and this value is very  
close to the sum of Ga and N sphere radii.

I think that my supercell is not very far from the  full relaxation,  
since the distances between Ga and N atoms as well as the distance  
between surface Ga atoms (next neighbors to N atom) and their inward  
shifts are very close to the values given in Phys.Rev. paper.

In spite of that, I still have the great desire to obtain the fully  
relaxed supercell and accordingly as precise STM image as possible.

Could you give me an advice:
1) are my suggestions reasonable?
2) Will the reduction of RMT(N) solve the problem?
3) Is it reasonable to renew the calculations with “partially relaxed”  
supercell as a starting structure (but of course with reduced value of  
RTM(N))?

Excuse me for so long letter.
Beforehand thankful,

Kakhaber Jandieri



Quoting Laurence Marks <L-marks at northwestern.edu>:

> Do grep -e :MIN *.ouptputM -- you need to keep going.
>
> On Thu, Jan 20, 2011 at 12:30 PM, Kakhaber Jandieri
> <Kakhaber.Jandieri at physik.uni-marburg.de> wrote:
>> Dear Wien2k users,
>>
>> Using "mini" I see the following message:
>>
>>>   stop
>>>   mini        (00:43:49) 0.880u 0.060s 0:01.25 75.2%  0+0k 0+4024io 0pf+0w
>>  :WARNING Please restart anew from final position
>>
>>>   stop forces small, minimization stopped
>>
>>>   relaxation steps summarized in Surface-GaAs-2N-b.scf_mini
>>
>>>   relaxed structure and results in Surface-GaAs-2N-b.struct, scf, clmsum
>>
>>>   please use   save_lapw save_file_name   to save the results
>>
>>
>> Could you explain what is the meaning of
>> "WARNING Please restart anew from final position"?
>>
>> I found a similar question in mailing list (Ghosh SUDDHASATTWA,  
>> /Sat Jul 24 05:54:54 CEST 2010) but unfortunately without any  
>> replied suggestions.
>>
>> Beforehand thankful,
>>
>> Kakhaber Jandieri
>> /
>>
>>
>> _______________________________________________
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>> Wien at zeus.theochem.tuwien.ac.at
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>
>
>
>
> --
> Laurence Marks
> Department of Materials Science and Engineering
> MSE Rm 2036 Cook Hall
> 2220 N Campus Drive
> Northwestern University
> Evanston, IL 60208, USA
> Tel: (847) 491-3996 Fax: (847) 491-7820
> email: L-marks at northwestern dot edu
> Web: www.numis.northwestern.edu
> Chair, Commission on Electron Crystallography of IUCR
> www.numis.northwestern.edu/
> Electron crystallography is the branch of science that uses electron
> scattering and imaging to study the structure of matter.
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
>



Dr. Kakhaber Jandieri
Department of Physics
Philipps University Marburg
Tel:+49 6421 2824159 (2825704)