[Pw_forum] specify correct q-point grid!

[Eyvaz Isaev]

Dear Max,

> IF (dos) THEN
> IF (nk1 < 1 .OR. nk2 < 1 .OR. nk3 < 1)
> & CALL errore ('matdyn','specify correct q-point grid!',1)

You correctly noticed that the error is due these lines. 
Because of that integration of DOS is done using the  tetrahedra method, so, there will be at least 1 tetrahedron with 4 points (vertexes). 

> ntetra = 6 * nk1 * nk2 * nk3 

This line (total number of tetrahedra) is due to the improved tetrahedra method by Bl\"ochl. You can find more in the original paper.

> nq1=3, nq2=3, nq3=2    ( in elph.in )

This q-points are not connected to DOS calculations in matdyn.x, they are for dynamical matrices D_{a,b}^{i,j}(q) calculations which then used to perform FFT to get real space F_{a,b}^{i,j}(R) force constants matrix.

You should use nk1,nk2,nk3 keywords in matdyn.in file for DOS calculations. By the way, most likely you did not specify these keywords which are zeros by default. Namely this one is stated in the abovementioned error.

Hope this helps,
Bests,
Eyvaz.

-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com


--- On Mon, 12/8/08, 陳 少華 <chen_shao_hua197 at yahoo.com.tw> wrote:

> From: 陳 少華 <chen_shao_hua197 at yahoo.com.tw>
> Subject: [Pw_forum] specify correct q-point grid!
> To: "Pwscf" <pw_forum at pwscf.org>
> Date: Monday, December 8, 2008, 10:04 PM
> Dear forum's members,
> 
> I do an el-ph calculation.
> The error message is
> 
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>      task #         0
>      from matdyn : error #         1
>      specify correct q-point grid!
> 
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> 
> So I examine the  espresso-4.0.3/PH/matdyn.f90
> ...
> IF (dos) THEN
>         IF (nk1 < 1 .OR. nk2 < 1 .OR. nk3 < 1)
> &
>              CALL errore  ('matdyn','specify
> correct q-point grid!',1)
>         ntetra = 6 * nk1 * nk2 * nk3
> ...
> 
> And I set
> 
> K_POINTS {automatic}
> 12 12 8 0 0 0           ( in scf.in )
> 
>   nq1=3, nq2=3, nq3=2    ( in elph.in )
> 
> I don't know why that error message show up and how to
> solve it ?
> 
> Thanks in advance
> Max
> Candidate of PhD
> Physics department, National Taiwan University, Taipei,
> Taiwan
> 
> 
> P.S. cat *.dyn0
> 
>    3   3   2
>    6
>    0.000000000000000E+00   0.000000000000000E+00  
> 0.000000000000000E+00
>    0.000000000000000E+00   0.000000000000000E+00 
> -0.337153960894342E+00
>    0.000000000000000E+00   0.338170830884862E+00  
> 0.000000000000000E+00
>    0.000000000000000E+00   0.338170830884862E+00 
> -0.337153960894342E+00
>    0.338170830884862E+00   0.338170830884862E+00  
> 0.000000000000000E+00
>    0.338170830884862E+00   0.338170830884862E+00 
> -0.337153960894342E+00
> 
> 
> 
> 
> 
>      
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