[Wannier] confusion on conductivity tensor calculation

[Jun Liu]

Dear wannier users,

I would like to ask whether the following input for conductivity tensor
calculation looks ok.

num_bands =   128  ! set to NBANDS by VASP
 num_wann =   88
 begin projections
 Mo:d    ! 20
 Te:p    ! 24
 end projections

###########BoltzWann ############
boltzwann = true
kmesh = 400 400 400
boltz_relax_time = 0.001
boltz_mu_min = 7.95123782                       #ef-def
boltz_mu_max = 8.35123782
boltz_mu_step = 0.04
boltz_temp_min = 2
boltz_temp_max = 10
boltz_temp_step = 2
boltz_tdf_energy_step=0.01
boltz_tdf_smr_fixed_en_width = 0.01
boltz_tdf_smr_type = gauss
boltz_calc_also_dos = true
boltz_dos_energy_min = 5.0
boltz_dos_energy_max = 15.0
boltz_dos_energy_step = 0.01
#################################

write_hr = .true.
# Bandstructure
 restart = plot
 bands_plot = true
 begin kpoint_path
....
 end kpoint_path
 bands_num_points 100 # bands_plot_format gnuplot


spinors = .true.

begin unit_cell_cart
     3.4716802     0.0000000     0.0000000  /*this and the next line
changes*/
     0.0000000     6.3666750     0.0000000  /*accordingly for different
cases*/
     0.0000000     0.0000000    13.8452386
end unit_cell_cart

begin atoms_cart
...
end atoms_cart

mp_grid =    12     6     3  /*this line differs from each case*/

begin kpoints
...
end kpoints

This input returns reasonable result (in that the conductivity tensor is
nearly diagonal for orthorhombic structure). But if I compare results
across different cases, they differ too much under as small as 0.5% lattice
constant change. More details are given below.

I tried to calculate the conductivity tensor with postw90.x with version
2.1. I tried it on three cases related with slight elongation along a or b
directions defining an orthorhombic structure on the original lattice. The
resulting conductivity tensor differs by nearly 100% for a 0.5% lattice
constant change, which cannot be right. To give you some numbers, the
following shows different sigma_x,x scanned under different chemical
potentials for different lattice structures, (other components of sigma are
suppressed for brevity but the whole sigma matrix does show a diagonal
feature expected for an orthorhombic structure.)

For the base structure (a,b,c)
    mu                      T                          sigma_x,x
   7.963542580       2.000000000      0.4228380355E-05
   7.963542580       4.000000000      0.6146815602E-01
   7.963542580       6.000000000       1.261398051
   7.963542580       8.000000000       5.250207712
   7.963542580       10.00000000       11.71261179

For the elongated structure along a by 0.5%
    mu                      T                          sigma_x,x
   7.962242580       2.000000000      0.5201871790E-03
   7.962242580       4.000000000      0.6688530829
   7.962242580       6.000000000       6.051666588
   7.962242580       8.000000000       16.35207686
   7.962242580       10.00000000       27.52636769

For the elongated structure along b by 0.5%
    mu                      T                          sigma_x,x
   7.951237820       2.000000000       332.9039665 <%28332%29%20903-9665>
   7.951237820       4.000000000       363.9745377
   7.951237820       6.000000000       287.1196636
   7.951237820       8.000000000       228.9187157 <%28228%29%20918-7157>
   7.951237820       10.00000000       188.4869745

Any idea on how to check the calculation? Thanks all very much for your
insightful help!

Sincerely,
Jun
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