[Wannier] Extracting the tight-binding elements from Wannier90

[Giovanni Pizzi]

Dear Alex,

Maybe this reply answers only partially to your questions, but anyway:

- to get the same interpolation, you should also use the content of the seedname_wsvec.dat file, see se. 8.21 of the user guide http://wannier.org/doc/user_guide.pdf as well as Sec. 9 “Some notes on the interpolation”

Anyway, the difference if you discard these elements should be small (the same as running with use_ws_distance=false or true).

For the non-diagonal elements at R=000: these would be hoping between different Wannier functions (that you project initially with different symmetry). The first option that comes to my mind: are the Wannier functions all at the same center? If not, this might be one cause for a non-zero element. Also, how big are these non-zero elements?

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 29 Apr 2018, at 23:09, Alex.Durie <alex.durie at open.ac.uk<mailto:alex.durie at open.ac.uk>> wrote:

Dear all,

Forgive the nature of this question, as I know there has been much previous discussion. I am new to Wannier90 and wish to extract the tight-binding parameters to use within my existing C++ code. I am attempting to compare against results that I have obtained using potentials within 'The Handbook of the Bandstructure of Elemental Solids' by D. Papaconstantopoulos.

I thought a good place to start would be bcc Fe spin up. To that end, I have started with input files from example08 with the following additions;


write_hr = true
use_ws_distance = true
bands_plot_mode = cut
dist_cutoff = 5

as I was hoping to use up to second nearest neighbour interactions, and wanted to check the bandstructure was sufficiently accurate.

I have attempted to use the relevant data within seedname_hr.dat to reconstruct the bandstructure in my C++ code to make sure I was building the Hamiltonians correctly and seem to be running into difficulty.

I assumed these were the lines of seedname_hr.dat that were relevant;


    0    0    0    n    m   real    imag
    1    1    1    n    m   real    imag
   -1    1    1    n    m   real    imag
    1   -1    1    n    m   real    imag
    1    1   -1    n    m   real    imag
   -1   -1    1    n    m   real    imag
    1   -1   -1    n    m   real    imag
   -1    1   -1    n    m   real    imag
   -1   -1   -1    n    m   real    imag
    2    0    0    n    m   real    imag
   -2    0    0    n    m   real    imag
    0    2    0    n    m   real    imag
    0   -2    0    n    m   real    imag
    0    0    2    n    m   real    imag
    0    0   -2    n    m   real    imag

but using these values does not yield the same bandstructure as that in iron_up_band.gnu.
Is there some form of reordering required that I have not considered?
Also, at R = 0,0,0 I am getting non-zero off-diagonal elements. Is that an error in output?

Also, I would have expected dist_cutoff = 2.942225 to be suitable to calculate the bandstructure up to second nearest-neighbour, but found that I needed dist_cutoff = 5 to observe non-zero second nearest-neighbour terms in iron_up.wout, under
     "Maximum absolute value of Real-space Hamiltonian at each lattice point"
unless I am misinterpreting the information?

Thanks in advance to anyone who can put me on the right track.

Alex Durie
PhD student
The Open University
United Kingdom

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