[Pw_forum] q not allowed

[Eyvaz Isaev]

Hi,

> trying phonon calculation, i used a small grid
> (331). but using q2r.x, the 
> code has given " q not allowed"
> in the archive i saw this:
> >there is a mismatch between what the q2r.x code
> thinks q-points should be, 
> >and what you provided.
Sorry, but quite stupid question: are these q-vectros
you used in cartesian or wrt basis vescors? As far as
I know q2r.x uses q-vectors in cartesian.
Besides, it might be that you specified insufficent
digits for q-vectors, so they  do not coincide with
those generated by q2r.x. 

> what should i do? so i have to forget this grid? how
> should i choose the  grid not to have this error?
> my case is base-centered tetragonal
The best way is using of the latest version of QE
where  you can specify nx,ny,nz in ph.in file so that
the program ph.x generates q-vectors and then
calculates dynamical matrices for thes q-points. The
next step is  FFT by means of q2r.x. See example 6.

Bests,
Eyvaz.



> thanx
> 
>
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