[Pw_forum] NSCF calculation and k-mesh inonsistency

[Giovanni Cantele]

Your system has 6 symmetry operations, as found in the output. Unless otherwise specified, pw.x always generates symmetry-inequivalent k-points, that is, if the k-point grid
is not compatible with the symmetry operations, it is automatically expanded so has to retrieve the crystal symmetry.

If you want to force pw.x to use the k-point grid you specify in the input as is use the variable (from Doc/INPUT_PW.txt):
   +--------------------------------------------------------------------
   Variable:       nosym

   Type:           LOGICAL
   Default:        .FALSE.
   Description:    if (.TRUE.) symmetry is not used. Note that
                   - if the k-point grid is provided in input, it is used "as is"
                     and symmetry-inequivalent k-points are not generated;
                   - if the k-point grid is automatically generated, it will
                     contain only points in the irreducible BZ for the bravais
                     lattice, irrespective of the actual crystal symmetry.
                   A careful usage of this option can be advantageous
                   - in low-symmetry large cells, if you cannot afford a k-point
                     grid with the correct symmetry
                   - in MD simulations
                   - in calculations for isolated atoms
   +——————————————————————————————————

Giovanni



> On 26 Nov 2015, at 16:34, Carlo Motta <MOTTAC at tcd.ie> wrote:
> 
> Hello,
> 
> I have been recently facing some problems occurring during a nscf calculation.
> As you can see in the input file nscf.in, I specify a grid of 216 kpoints, but the codes performs the calculation over a different grid made of 424 kpoints, which contains and expands the one I included in nscf.in (see grid.jpeg attached).
> 
> I am naively assuming that something went wrong - this is not what I would expect. Also, I need this calculation to wannierize some bands and the postprocessing tool pw2wannier90.x, that I run after the nscf, gives an error, which I suspect to be related with the mismatch in kgrids.
> 
> Thank you in advance,
> 
> --
> 
> Carlo Motta
> 
> PostDoc Researcher
> School of Physics and CRANN,         
> Trinity College Dublin,                         
> Dublin 2, IRELAND
> <out.nscf><nscf.in><kgrid.jpeg>_______________________________________________
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele