[Wannier] periodicity of Mmn in the Brillouin zone

[marcin.kurpas at us.edu.pl]

Dear Wannier90 developer and users, 

I want to calculate overlaps  of the periodic functions <u_nk|u_nk'> ,
where k is fixed and  k'  runs over the whole first Brillouin zone of a
2D material to compare with a tight binding model.   Only a single band
is considered.  I generated a k-point grid using kmesh.pl, run scf, nscf
calculations in Quantum Esrpresso and did wannier90 preprocessing. 

To run pw2wannier I generated pairs of k-points entering the nnkpts
block so that they include couplings between all k-points  form the
first BZ with each other (b-vector was always 0): 

begin nnkpts
N*N
1 1 0 0 0
1 2 0 0 0
...
1 N 0 0 0
...
...
N 1 0 0 0
....
N N 0 0 0
end nnkpts 

where N is the numer of kpoints in FBZ. When I plot the overlaps |<u_nk|
u_nk'>|^2  file in the FBZ, where k is fixed and k' runs over the whole
BZ, the picture I get is not periodic, that is, when I replicate the BZ
in kx and ky dimensions the full picture does not look like a smooth
varying function but has step-like sharp changes at the border of BZ
that do not fit each other. In contrast, the tight-binding model gives a
periodic image.  

Shall I sum contributions |<u_nk| u_nk'(b) >|^2 of all b_k vectors from
all shells to get the periodic image?
I would appreciate your help on this question. 

Best regards,  

Marcin Kurpas
Institute of Physics
University of Silesia in Katowice
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