[QE-users] How to calculate tangential interband matrix element along a closed loop

[Paolo Giannozzi]

If you compile QE with HDF5 support, binary data files are written in HDF5
and readable using external software (e.g. python scripts). Fortran
binaries are readable only from fortran.

Paolo

On Mon, Sep 20, 2021 at 8:24 PM Tharindu W-fernando via users <
users at lists.quantum-espresso.org> wrote:

> Hello Everyone,
>
> The common interband matrix element <m| dH/dkx \pm i dH\dky |n> seems to
> be calculable using DFT software. However, I am trying to calculate the
> tangential matrix element <m| dH/dt | n> \equiv <m| dH/dkx dkx/dt + dH/dky
> dky/dt |n> for some parameter t that parameterizes a closed loop in
> k-space: (kx(t),ky(t)) = (kx0+cos(t), ky0+sin(t)), where the loop center is
> (kx0,ky0). With my basic understanding of QE, I thought of a way to do this
> using a monolayer MoS2 example:
> I first sample k-points along a closed loop. This gives me wavefunctions
> in the .dat format. I was hoping to somehow extract wavefunction data to
> smoothen the gauge using the maximally localized Wannier function method,
> and manually calculate the matrix element I want using a central difference
> method with MATLAB or Python.
> However, I cannot seem to read the data from the .dat files. I saw several
> solutions in the archives that suggest using different existing routines
> that involve the evec variable. However, I am not familiar with Fortran90
> and so have trouble figuring out how exactly to use such routines and
> custom code to get eigenvector data in a readable format. Does anyone have
> any advice or resources? I am using QE v6.6
> Alternatively, are there other more-direct ways to go about calculating
> the quantity I want?
> Thank you very much for your time!
>
> Tharindu W. Fernando
> PhD Student, University of Washington
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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