[Pw_forum] Fwd: different symmetry when using equivalent representation

[Jess Kondor]

On Thu, Dec 17, 2009 at 11:04 AM, Lorenzo Paulatto <paulatto at sissa.it> wrote:
> Replying to message "[Pw_forum] Fwd: different symmetry when using
> equivalent representation" from Jess Kondor (17/12/09):
>>  I have some trouble in understanding why equivalent (if I am not
>> wrong) representation of the crystal structure leads to different
>> symmetry (as shown in the output from pw.x). All input/output
>> files are attached.
>
> Dear Jess,
> the code threshold for checking the symmetry is too strict for the number
> of significant digits you have specified for the basis vectors (I see you
> have copied them from the output of test1.inp, but apparently it is not
> enough).
>
> You recover all 6 symmetry operations if you specify the cell parameters
> with more digits, e.g.
>    0.502718227240668  -0.290244503823931   0.814268083618657
>    0.000000000000000   0.580489007647862   0.814268083618657
>   -0.502718227240668  -0.290244503823931   0.814268083618657
>
> best regards
>
> --
> Lorenzo Paulatto
> SISSA  &  DEMOCRITOS (Trieste)
> phone: +39 040 3787 511
> skype: paulatz
> www:   http://people.sissa.it/~paulatto/
>
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Dear Lorenzo,

 Thanks a lot for the solution. How many digits do I need? I agree,
that output basis vectors are printed with 6 significant digits and
this is not enough. However, if I change 'scf' to 'vc-relax', the code
prints CELL_PARAMETERS with much more digits (9), and this is still
not enough to find all 6 symmetries.

   0.502718227  -0.290244504   0.814268084
   0.000000000   0.580489008   0.814268084
  -0.502718227  -0.290244504   0.814268084

Probably,  it is better to change a source code to print more digits
in order to allow simple cut/and/paste from output/to input without
using extra tools?

Thanks a lot!


-- 
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Jess Kondor

NSTI
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