[Pw_forum] Kponts generation from kpoint.x

[Gabriele Sclauzero]

vtmtrinh at caltech.edu wrote:
> Dear PWSCF Users,
> 
> I also checked prevoius discussions in PWSCF forum.  pw.x also takes into
> consideration of the crystal symmetry, while kpoint.x uses lattice
> symmetry.  (My studied system is body-cntered tetragonal cell). It seems
> that I could not use the kpoints list given by kpoint.x.   If I would like

You got the point!

> to obtain a whole list of kpoints (consistent with those generated by
> pw.x), how could I do so?

I'm not sure that your request is totally clear to me. If you want the full list of 
k-points, without any symmetry reduction, you can use kpoints.x: it has an option which 
prints on output the full list, together with an index which tells you if there is in the 
list another k-point which is equivalent by symmetry.
I think you could even generate the mesh "by hand" in crystal coordinates: it is a 
regularly spaced grid in a three dimensional cube, possibly shifted from the origin.
Give a look inside PW/kpoint_grid.f90:

   do i=1,nk1
      do j=1,nk2
         do k=1,nk3
            !  this is nothing but consecutive ordering
            n = (k-1) + (j-1)*nk3 + (i-1)*nk2*nk3 + 1
            !  xkg are the components of the complete grid in crystal axis
            xkg(1,n) = DBLE(i-1)/nk1 + DBLE(k1)/2/nk1
            xkg(2,n) = DBLE(j-1)/nk2 + DBLE(k2)/2/nk2
            xkg(3,n) = DBLE(k-1)/nk3 + DBLE(k3)/2/nk3
         end do
      end do
   end do

However maybe there is no need to do this if you simply want to run a nscf calculation on 
a full 3D grid of k-point; try with

nosym=.TRUE.
noinv=.TRUE.

It should disable any symmetry reduction in the generation of the k-point list (but also 
symmetrization of charge).



HTH

GS



> 
> Thank you,
> 
> Trinh
> 
>> Dear Pwscf,
>>
>> I run a nscf calculation with k-point grid of 12x12x12 (automatic).  From
>> the output of pw.x, I saw 163 kpoints were generated and computed.  Since
>> I would like to get the whole 3D-band structure, I run kpoint.x to get
>> other kpoints.  A number of kpoints generated by pw.x (for the nscf
>> calcultion) could be found te coincide with those generated by kpoint.x.
>> However, there many kpoints generated by pw.x could not found in the
>> output of kpoint.x.  I am not sure about the reason why there is the
>> difference here: Is it due to reverse symmetry or something else?   I
>> appreciate very much if you could tell me why.
>>
>> Best,
>>
>> Trinh Vo
>>
>> JPL/CalTech
>>
>>
>>
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> 
> 
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