[Pw_forum] NSCF calculation and k-mesh inonsistency
Giovanni Cantele
giovanni.cantele at spin.cnr.it
Thu Nov 26 16:45:51 CET 2015
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
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