[Wannier] confusion on conductivity tensor calculation
Jun Liu
jun.physics at gmail.com
Sun Jun 25 05:23:03 CEST 2017
Dear Prof. Giovanni,
Thank you very much for your help. I do need to see how conductivity
changes across the three cases I mentioned under T=2K. But I should be
satisfied with the trend of change if the results look reasonable at higher
T. I have submitted jobs for T=50K and see how they will work out (still
not finished yet).
Could you please elaborate on what you mean by numerical and convergence
issues? I think I should have at least reached K-points and ENCUT
convergence.
Thanks,
Sincerely,
Jun
On Thu, Jun 15, 2017 at 12:24 PM, Giovanni Pizzi <giovanni.pizzi at epfl.ch>
wrote:
> Dear Jun,
> You are working in the range of temperatures 2-10 K. Is this expected?
> Such low temperatures are very hard to work with in the code, because of
> numerical and convergence issues.
>
> If you work at higher temperature, is the result better?
>
> Also, remember that by changing the strain you will change the energy
> position of the bands (as basically all materials have non-zero deformation
> potentials) and therefore you cannot really compare values at the same
> exact chemical potential mu. E.g. it is possible that when you get close to
> zero, it is because at that strain there’s no band close to the chemical
> potential (and since you are at low T, you need bands really close).
> Changing strain, bands enter in the region.
>
> I suggest that you start by T>50K (and without
> boltz_tdf_smr_fixed_en_width) and you compare the whole plots in a chemical
> potential range, and once you understand the behaviour you go down in
> temperature, potentially putting back some smearing in the TDF, to check
> also if you are converged enough. Note however that the TDF smearing while
> probably needed at low T, might introduce some errors in the final results.
>
> Hope this helps,
>
> Giovanni
>
>
>
> --
> Giovanni Pizzi
> Theory and Simulation of Materials and MARVEL, EPFL
> http://people.epfl.ch/giovanni.pizzi
> http://nccr-marvel.ch/en/people/profile/giovanni-pizzi
>
> On 31 May 2017, at 18:42, Jun Liu <jun.physics at gmail.com> wrote:
>
> 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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