[Pw_forum] Re: q not allowed (Katalin Gaal-Nagy)

[Eyvaz Isaev]

Hi Katalin,

My apologies for very stupid question: did you change
nq's in q2r input file?

I still prefer 2.1.5 (rather old) version and there is
not too much difference in q2r.x between 2.15 and
3.1.1 versions.  So, do not worry about your q2r (and
PWSCF) version. 

I use this procedure last 4 years and never met any
problem for any lattice structure I considered (bcc,
fcc, hcp, bct, orthorhombic, sc), except ibrav=0
though this case is also no problem. 
And once for hcp lattice I used quite unusual choice
of basis vectors, and forgot about it that led to this
erros.  

Bests,
Eyvaz.
--- Katalin Gaal-Nagy
<katalin.gaal-nagy at physik.uni-regensburg.de> wrote:

> Dear Eyvaz,
> 
> thanks for the reply.
> 
> I know that it was explained before, and I generated
> the q points exactly 
> in that way: Running pw.x for some minutes (the q
> points have the correct 
> units, etc, thanks Cesar for the hint!), take the q
> points and put them 
> to the phonon calculation. It worked well with the
> 4x4x4 mesh.
> For the 4x4x8 mesh I did the same, compared the two
> grids and calculated 
> just the q points which have been missing. And there
> the error appeared 
> for some (not all) of the new q points.
> 
> For curiosity, I just removed the not-allowed q
> points from the files, but 
> then there are some q points missing. At the moment
> I guess that due to 
> some symmetry operation some signs of the q points
> are changed, or, 
> translated to other IBZs, whatever, and I want to
> look through the q2r 
> routine and print out the "reference" q points and
> compare them with the q 
> points I have in the files with the dynamical
> matrices. Then I will see 
> what is going on. (I still use the "old" version of
> the q2r).
> 
> Unfortunatly, I am not at the office for one week,
> but I will give a short 
> report as soon as I have some news.
> 
> All the best,
> Katalin
> 
> 
> > Hi,
> >
> > Sorry interfering in, but it was explained before
> why
> > this happens. Let me remind again.
> >
> > In my opinion, there is two solutions of the
> problem:
> >
> > 1) use >v3.0 where you can directly put  nq1, nq2,
> nq3
> > and everything will go smoothly:
> > (something like this:)
> > &inputph
> >  tr2_ph=1.0d-14,
> >  prefix='C8',
> >  ldisp=.true.,
> >  nq1=4, nq2=4, nq3=4
> >  amass(1)=12.01,
> >  outdir='$TMP_DIR/',
> >  fildyn='C8.dyn',
> > /
> >
> > In this case you have to supply enough CPU time to
> > complete dynamical matrix calculations. Otherwise
> in
> > some clusters you will lose your temporary files
> and I
> > am not sure that an option "recover" will help in
> this
> > case. I would be happy if this one is not true. In
> > fact, I faced this problem.
> >
> > 2) If you prefer say 2.1 version, again, it was
> > explained before, and the best way is to generate
> > q-points via pw.x (kill the job in few seconds and
> > look at *.scf.out file) and put them into your
> input
> > file.
> > In this case the \Gamma point is calculated
> separately
> > and, thus, remove the \Gamma point from the list.
> >
> > Hope they are helpful.
> >
> > Bests,
> > Eyvaz.
> >
> > --- cesards at msi.umn.edu wrote:
> >
> >> A common cause for this problem is defining
> q-points
> >> in reciprocal cell
> >> coordinates. q-points must be defined in 2pi/a
> >> ccoordinates.
> >>
> >> Yours,
> >>
> >> Cesar R.S. da Silva
> >>
> >>
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