[Wien] finding theta(G) in the source of code

[fatemeh.mirjani]

Dear all;

My problem is finding theta(G) (The Fast Fourier Transform of a step-function. I call the step-function theta(r) and it is equal to zero in the spheres and is equal to 1 at the interstitial region. G is the reciprocal lattice vector.)

I need theta(Gi-Gj) [the FFT of the step-function] to calculate the overlap matrix:

                 M_mn interstitial(k1,k2)=<u_m,k1|u_n,k2>= sigma_ij{c*_m,k1(Gi) * theta(Gi-Gj) *  c_n,k2(Gj)}

M is labeled by m,n (band index) and k1,k2 (k-points).

 
I think I should find out a variable equivalent with theta(Gi-Gj) from the source of code in order to accomplish my interface code between Wien2k and Wannier90.
1-Would you please guide me which variable in the source is equal to theta(Gi-Gj)? and where is it?
2-How is clarified the dependence of theta to (Gi-Gj) in the source of code?

I'm anxiously looking forward your reply and guidelines.

With my best regards,
Fatemeh

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|Fatemeh Mirjani                              | Email: f_mirjani at ph.iut.ac.ir  |
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