[Pw_forum] symmetry identification

[Stefano Baroni]

Dear W Yu: this problem has been discussed zillions of times in this  
forum, and has to do with the commensurability of fractional  
translations with the FFT grid. Please, refer to archive where, I am  
sure, you will find the answer to your question. Also, please note  
that we really appreciate those posts to this mailing list which are  
thoroughly signed (name, current affiliation). Thanks a lot for using  
QE and for posting to this mailing list. Stefano Baroni

On Jun 25, 2007, at 10:03 AM, W. YU wrote:

> Dear PW users,
>
> I met a problem when doing some calculation on a body
> centered tetragonal structure. The space group no. is
> 139 (I4/mmm). There are all together 16 symmetry
> operations, but pw can only identify 8 symmetry
> operations without inversion. So in a follow up phonon
> calculation, the given phonon symmetry modes are not
> consistent with the space analysis. I an not sure
> whether the lost symmetry operations are caused by the
> input coordinates. I tried it with wie2k package, it
> could identify all the symmetry operations. So what
> could be the cause for this problem? The input file is
> attached. Any help would be much appreciated. Thanks.
>
> Wen Yu
>
>  =====================================================
> The following is my  input file:
>
>  &system
>     ibrav = 7, celldm(1) =7.1747,celldm(3)=3.2818,
>     nat= 7, ntyp= 3,
>     ecutwfc = 50.0,ecutrho = 400.0,
>     occupations = 'smearing',
>     smearing = 'methfessel-paxton',
>     degauss = 0.02,
>   /
>  &electrons
>     mixing_beta = 0.2
>  /
> ATOMIC_SPECIES
>  Sr  87.62  Sr.pbe-nsp-van.UPF
>  Cu  63.55  Cu.pbe-n-van_ak.UPF
>  O   16.0   O.pbe-van_ak.UPF
> ATOMIC_POSITIONS bohr
>  Sr 0.0 0.0  8.341471850
>  Sr 0.0 0.0  15.20471415
>  Cu 0.0 0.0  0.0
>  O  0.000000 3.587363  0.0
>  O  3.587363 0.000000  0.0
>  O  0.0 0.0   3.64071128
>  O  0.0 0.0  19.90547472
> K_POINTS automatic
> 8 8 8 0 0 0
> EOF
>
>
>
>
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

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