K-ponit in nl calculations

[sdwang]

Dear developer,
I am running nl calculations with Lumen for two different hexagonal 2D systems, and both of them have 6 Sym. Ops. (no inversion) in the nscf output of QE. However, when I switch to the shift current calculations with ypp_nl to remove the symmetry, one system have 900 k points in the FixSymm/SAVE directory while another one has only 465 k points (for both systems in nscf, I set 30x30x1 k points and both of them have irreducible k points of 91 in the nscf.out, and both have the same parameter as:

Code: Select all

% Efield1 
0.000000 | 1.000000 | 0.000000 |  # First external Electric Field
%

My question is why the same symmetric systems have different k point for nl clculations? Except for the symmetry, what other parameters influence the k points in nl since this requires much more time and memories...

Thanks!

Shudong

[claudio]

Dear Shudong

This is really puzzling to me. If they have the same symmetries and the same number of k-points in the IBZ,
when you remove the symmetries, shouldn't they still have the same number of k-points.
Please provide an example and I will take a look.

best
Claudio

[Davide]

It seems that in one case there are residual simmetry operations which leave invariant the field along y.

Can you copy and paste here the log of your ypp output when removing symetries?

[sdwang]

Dear Davide,
Here is the input:

Code: Select all

# $$ |     $$   $$ $$$$$$$$$$   $$$$$$  $$$$$$$
# $$ |     $$ |  $$ |$$  _$$  _$$ $$  __$$ $$  __$$
# $$ |     $$ |  $$ |$$ / $$ / $$ |$$$$$$$$ |$$ |  $$ |
# $$ |     $$ |  $$ |$$ | $$ | $$ |$$   ____|$$ |  $$ |
# $$$$$$$$\$$$$$$  |$$ | $$ | $$ |$$$$$$$ $$ |  $$ |
# ________|______/ __| __| __| _______|__|  __|
#
#                   Fork Lumen 2.0.0
#                       Branch is
#           MPI+OpenMP+SLK+HDF5_MPI_IO Build
#               http://www.lumen-code.org
#
fixsyms                          # [R] Remove symmetries not consistent with an external perturbation
% Efield1
 0.000000 | 1.000000 | 0.000000 |        # First external Electric Field
%
% Efield2
 0.000000 | 0.000000 | 0.000000 |        # Additional external Electric Field
%
BField= 0.000000           T     # [MAG] Magnetic field modulus
Bpsi= 0.000000             deg   # [MAG] Magnetic field psi angle [degree]
Btheta= 0.000000           deg   # [MAG] Magnetic field theta angle [degree]
#RmAllSymm                     # Remove all symmetries
RmTimeRev                     # Remove Time Reversal
#RmSpaceInv                    # Remove Spatial Inversion
#KeepKGrid                     # Do not expand the k-grid

and the attached are the output files of the two with reduced and full k-points.

Thanks!

Shudong

[Davide]

As you can see from the report, in the case with 465 points, the symmetry which sends x --> -x is still present.

This is correct, since a field along y is invariant under such operation.

Best,
D.