[Wien] 2- overlap matrix at the interstitial region and using FFT

[fatemeh.mirjani]

Dear all;

I need theta(Gi-Gj) [the FFT of the step-function at the interstitial region] to calculate the overlap matrix which I mentioned in my previous email.
                 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) and G is the reciprocal lattice vector.
 
According to my search in mailing-list, I think that is related to SRC_lapw0/rean files where they use FFT method. but I cannot find out a variable euivalent with theta(Gi-Gj) from the source 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?

Your help is appreciated like your previous favor.

With my best regards,
Fatemeh
-- 
+------------------------------------------------------------------------------+
|Fatemeh Mirjani                              | Email: f_mirjani at ph.iut.ac.ir  |
|Computational Condensed Matter Research Lab. | Tel/Fax Office: +98311-3913746 |
|ICTP Affiliated Center in Isfahan,           | Tel Lab.: +98311-3913731       |
+----------Physics Department, Isfahan University of Technology, Iran----------+