[Wien] source code question : hamilt.F

[Alessandro Mirone]

Dear Wien users and developpers,

  I have studied almost every single line of lapw0 and lapw1.
In the following peace of code

!_COMPLEX               HPANEL(J,IHELP) = X2* SPANEL(J,IHELP) + &
!_COMPLEX                                 WARPIN(KZZ(1,J)-KZZ(1,I), &
!_COMPLEX                                        KZZ(2,J)-KZZ(2,I), &
!_COMPLEX                                        KZZ(3,J)-KZZ(3,I))

a contribution for H matrix element from wave J to wave I is calculated.
Therefore I was expecting WARPIN(K(I)-K(J)) to be used.
But that's not the case. Why?
What do I have wrong ?
Regards
    Alessandro Mirone