[Wien] bulk and surface DOS's discrepancy

[Javad hashemifar]

Hello

Based on our experiences on GaAs thin films, I think it is not so easy
to retain accurately the semiconducting character of materials in the
middle of slabs and some times (or even usually) there are some long
range surface states that fill the gap of middle layer DOS.
But hopefully this would not be a problem for most of your surface
results. For example the total energy of your system (and relating
properties) are most likely reliable for slabs with more than 7-8
layers.

Best regards
Javad Hashemifar

On 11/26/06, morteza rafiee <m_rafiee_k at yahoo.com> wrote:
> Dear Wien users.
> I have created a surface with several layers. The number of our layers is
> comparable with the number of layers used by others. We except that the
> physical properties of our middle layers are similar to the bulk properties.
> Hence we expect to obtain similar electronic structures for both the middle
> layers and bulk within our calculations. To keep the same accuracy the
> density of k-points in the bulk and surface calculations were taken to be
> equal. We have not yet relaxed the atoms in the surface. We have compared
> the total density of states (DOS's) of a selected atom in the bulk with the
> similar atom in the middle layer. The comparison shows that they are not
> exactly compatible with each other. For instance the DOS of the bulk shows
> insulator behavior. This is in the case that the DOS of the atom in the
> middle layer shows a metallic behavior. We have observed that the metallic
> behavior approaches to the insulator behavior by increasing the number of
> layers. However, neither our facility does allow us increasing the number of
> layers more than this (10-pair-layers=20 layers) nor the calculations of the
> others suggest such an increasing towards such extremely heavy calculations.
> I do not know if the relaxation of the layers will fix the problem or not.
> We also not aware whether this is a usual problem in surface calculations or
> we must try to reach exactly the bulk DOS.
> I will be thankful to every body who help me.
> Your.
> Morteza Rafiee.
>
>
>
>
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-- 
===========================
Javad Hashemifar,   Ph.D. in Physics
Tel:  +98-311-3912375
Fax: +98-311-3912376
Physics Department, Isfahan University of Technology, 84156, Isfahan, Iran
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