[Pw_forum] vc-relax with BFGS

[Gabriele Sclauzero]

On 02/14/2011 03:54 PM, Srijan Kumar Saha wrote:
>
>
> Dear Gabriele,
>
> Thank you very much for your kind reply.
>
> > Where did you get this information from? Was it printed by the code?
> I never saw a printout of the "Final symmetry", but maybe I am wrong
> and the code computes and prints it. Which version of the code are you 
> using?
>
> I am using the 4.2 version of the QE code and I have obtained the 
> Final symmetry
> simply feeding back the final positions and final cell parameters in a 
> brand new relax calculation.
> Then, in the beginning of this new run, the QE prints the symmetry again.

OK, but how are you building the new input? If you want to use the 
atomic positions as supplied in your previous email
e.g.
    0.000000000   0.000000000   0.000000000
    0.250189867   0.250189867   0.250189867
    0.000000000   0.250189689   0.250189689
    0.250189689   0.000000000   0.250189689
    0.250189689   0.250189689   0.000000000
...
you have to use CELL_PARAMETERS as supplied from the output of vc-relax, 
and ibrav =0
For me it works using:
CELL_PARAMETERS
1.000758849 0.0 0.0
0.0 1.000758849 0.0
0.0 0.0 1.000758849
guessing the celldm expansion from your final positions.

Another solution would be to use the final celldm(1) and rescale the 
atomic positions.

BTW, during relaxations the code checks at each step if the initial 
symmetry is conserved. If the symmetry had changed during the run the 
code would have stopped with an error message.


Regards,

GS


> Moreover, I have cross-checked the above symmetry with another 
> symmetry tool called ISOTROPY.
>
> Thanks and regards,
> Srijan K.
> CCMT
> Indian Institute of Science
> India 560012
>
>
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-- 

Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne

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