[Pw_forum] Point group changes when I modify ecutrho

[Bahadır SALMANKURT]

Dear Paolo

Thanks for reply.

Bests

2016-06-10 15:55 GMT+03:00 Paolo Giannozzi <p.giannozzi at gmail.com>:

> See 5.0.0.19 and 5.0.0.20 in the user guide of PWscfs:
>
> http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/node20.html#SECTION000600190000000000000
> in particular this:
>
> * they contain a fractional translation that is incompatible with the
> FFT grid (see next paragraph). Note that if you change cutoff or unit
> cell volume, the automatically computed FFT grid changes, and this may
> explain changes in symmetry (and in the number of k-points as a
> consequence) for no apparent good reason (only if you have fractional
> translations in the system, though).
> [...]
>
> 5.0.0.20 Warning: symmetry operation # N not allowed
>
> This is not an error. If a symmetry operation contains a fractional
> translation that is incompatible with the FFT grid, it is discarded in
> order to prevent problems with symmetrization. Typical fractional
> translations are 1/2 or 1/3 of a lattice vector. If the FFT grid
> dimension along that direction is not divisible respectively by 2 or
> by 3, the symmetry operation will not transform the FFT grid into
> itself. Solution: you can either force your FFT grid to be
> commensurate with fractional translation (set variables nr1, nr2, nr3
> to suitable values), or set variable use_all_frac to .true., in
> namelist &SYSTEM. Note however that the latter is incompatible with
> hybrid functionals and with phonon calculations.
>
> On Fri, Jun 10, 2016 at 1:58 PM, Bahadır SALMANKURT
> <bsalmankurt at gmail.com> wrote:
> > Dear All,
> >
> > I have been calculating structure parameter of ZrBeSi type crystal, whose
> > point group is D6_h. When I take ecutrho as 500 Ry, everything is ok. But
> > When I decrease ecutrho from 500 to 480 , its point group become D3_d
> even
> > if crystal_sg is used.
> >
> > Why does such a thing happen?
> >
> > Thanks in advance
> > --
> >
> > Bahadır SALMANKURT
> > Ph.D. Candidate
> > Department of Physics, Sakarya University, TURKEY
> >
> > _______________________________________________
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> > Pw_forum at pwscf.org
> > http://pwscf.org/mailman/listinfo/pw_forum
>
>
>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
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-- 

Bahadır SALMANKURT
Ph.D. Candidate
Department of Physics, Sakarya University, TURKEY
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