[Wien] How to assign kz to slab bands?

[pluto]

Dear All,

Everyone who has done a slab calculation knows that it contains some 
surface states and some projected bulk bands.

These projected bulk bands are typically nearly identical to the bulk 
projected bands. If we have a 10ML slab, they will essentially look like 
cutting the bulk BZ 10 times along kz. In case of bulk bands obviously 
each cut is assigned to some kz.

Now, we can compare bulk projected bands and slab bands, and then we 
will more or less know which of the slab bands relate to which kz 
(besides the surface states that don't have kz).

Is there a simple way to automatically assign kz to the slab bands?

One solution to this problem would be to calculate something like 
<exp(ikz.r)|Psi(k_paral,E,r)>, which is essentially a Fourier transform 
of the initial wave function for some energy and k_paral, i.e. for one 
eigenvalue point in the band structure. Is that kind of matrix element 
hidden somewhere in the WIEN2k output files?

Actually, this would also assign kz to the surface states, which could 
also be useful in the photoemission context.

Best,
Lukasz