Dear Robert and all,
Thanks for your email. Indeed, the quantity I am looking for does not depend on the value of Kz. The main issue is that the Mmn matrix should calculate on a Kx-Ky plane with any arbitrary Kz. Please look at the fallowing input files and let's me know if it's right or wrong.
Hope to receive your comments.
*****************************************************
num_bands         =   12        
num_wann          =   8 

!spinors = true
begin projections
Si : sp3
end projections


one_dim_axis = z
dist_cutoff_mode = two_dim
dist_cutoff = 9.76
devel_flag=kmesh_degen 
skip_B1_tests = .true.

begin unit_cell_cart
bohr
-5.1000 0.0000 5.1000
 0.0000 5.1000 5.1000
-5.1000 5.1000 0.0000
end unit_cell_cart

begin atoms_frac
Si   0.00   0.00   0.00 
Si   -0.25  0.75  -0.25
end atoms_frac

mp_grid           = 8  8  1

begin kpoints
  0.00000000  0.00000000  0.00000000  1.562500e-02 
  0.00000000  0.12500000  0.00000000  1.562500e-02 
. . .
end kpoints
*************************************************
Best, 

Ali Dehghan
Shiraz university, Iran