[Wien] problem on electronic structure in slab

[Aaron]

Dear Professor Blaha,


    Thank you very much for your reply!

Best wishes,
Aaron

On Wed, Aug 3, 2011 at 6:10 PM, Peter Blaha <pblaha at theochem.tuwien.ac.at>wrote:

> You have a small misconception.
>
> Of course, if there is a state which is located somewhere (either at  the
> surface or in the
> bulk), this state interacts with ALL other atoms. Eventually this
> interaction will be small,
> but unless it is forbidden by symmetry, it will be there.
>
> Thus if your surface layer has some DOS, the central layer MUST also have
> some (eventually small)
> DOS. It is your responsibility to judge weather this is a "negligible"
> contribution (as you said, 10^-5)
> or if it is sizable. If it is negligible, you still can interpret your
> results as being
> halfmetallic in the bulk, but metallic at the surface .....
>
> Am 29.07.2011 10:25, schrieb 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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>>
>
> --
>
>                                      P.Blaha
> ------------------------------**------------------------------**
> --------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
> Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/**
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