[Wien] problem on electronic structure in slab

[Aaron]

Dear wien2k developers and users:

    I've performed a calculation on a slab. My original purpose is to
investigate the surface electronic structure, which should be different from
the bulk one in my thought. The supercell is composed of a slab consisting
17 atomic layers and vacuum of 12 angstrom between periodic slab arrays. PBE
parameterization of density functional has been used in calculation.
    To my surprise, an unusual phenomena has been found in DOS (density of
states) result that the position of valence band maximum (VBM) at surface
and central layer are exactly the same. Actually, VBM in all LDOS (layer
density of states) are precisely at the same energy position. Of course, the
shape of DOS varies in different layers. But the edge of DOS peak are
aligned to the same energy position from surface to central layer. That is
to say, if DOS at a energy is zero in one layer, it will be zero at any
other layer. And if DOS at a energy is not zero in one layer, it will never
be zero at any other layer, even as small as 10^-5, but never would it be
zero.
    This phenomena brings a trouble that transitions such as metal to
insulator or half-metal to metal from bulk to surface cannot be simulated in
my slab model. For example, result (de Wijs and de Groot, PRB, 64, 020402)
on (111) slab of NiMnSb cannot be well reproduced in my calculation, because
DOS at the Fermi level in minority spin channel at central layer is not
absolute zero in my result although it is very small.
    So I post this letter here, asking for help. Is it a character of result
from DFT program that DOS at different layer in a slab have the same edge,
or did I make my calculation wrong?

Sincerely yours,
Aaron
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