[QE-users] k point symmetry and open_grid.x error

[Lorenzo Paulatto]

In theory it should be possible to obtain what you need, but it is not
simple. The current open_grid code abuses some subroutine from the exact
exchange calculation, which apply symmetry to wave functions but do not do
any kind of k->k+G transformation to bring them inside the first unit cell.
Rewriting all the machinery (with all the special cases: spin, noncolinear,
parallelism, etc. ) would take a lot of time..

-- 
Lorenzo Paulatto

On Sat, Feb 5, 2022, 22:28 Zeeshan Ahmad <azeeshan at uchicago.edu> wrote:

> Hi,
>
> The open_grid.x code with automatic grid of k points in the scf input file
> produces k points between -0.5 and 0.5 (crystal coords). However, the EPW
> code requires wave functions for full set of k points from 0 to 1 in the
> first BZ and gives an error when using k points between -0.5 and 0.5:
>
> Error in routine epw_setup (1):
> coarse k-mesh needs to be strictly positive in 1st BZ
>
> Unfortunately this is a hybrid functional calculation, so I cannot perform
> nscf calculation or use all k points in scf due to high memory requirement.
>
> Therefore, I tried using the kpoints.x code in the PW/tools to generate
> IBZ k points between 0 and 1 and specified the weights in scf file. On
> running open_grid.x on this calculation, I get the error:
>
> Error in routine exx_grid_init (1):
>      wrong EXX q grid
>
> Is it not possible to use open_grid.x other than for automatically
> generated k-points (runs fine in that case)? And is there a way to generate
> the files for full set of k-points between 0 and 1 instead of -0.5 and 0.5?
>
> The files for reproducing the error are at:
> https://gitlab.com/ahzeeshan/qe-issues/-/tree/master/open_grid
>
> I used a 4 by 4 by 2 grid of k-points to generate the IBZ using kpoints.x
> code.
>
> Thanks for your help,
> Zeeshan
>
>
>
>
> --
> Zeeshan Ahmad
> Postdoctoral Scholar
> Pritzker School of Molecular Engineering
> The University of Chicago
>
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