[DFTB-Plus-User] Fermi energy for surface

Vladimir Yushkevich yushkevich.v.n at gmail.com
Tue Mar 1 16:56:08 CET 2011

Dear Bálint

Yes I think so (but I have to check it). In my previous band structure
calculations I found that the DOS picture shifted due to the changes in
supercell vector (I think that the shift of Fermi level has the same value,
because band gap is unchanged). But I interested in absolute value of Fermi
level for surface. Can I shift my valence band for surface to the valence
band for bulk and conclude that the Fermi level for surface also changes
with respect of such shift?

Best regards, Vladimir

2011/3/1 Bálint Aradi <balint.aradi at bccms.uni-bremen.de>

> Hi,
> > I have following issue. My system is slab of titanium dioxide surface and
> I
> > have found that by increasing the supercell size in nonpereodic direction
> > (increasing the thickness of vacuum layer between two repeated slabs) the
> > obtained Fermi energy also increases. In slab approximation the vacuum
> layer
> > should be thick enough but I really confused in choice of it. The slab
> > thickness is ~ 16 Å and for two different supercell heights of ~50 Å and
> > ~100 Å the corresponding Fermi energies are 3.2 eV and 3.6 eV
> respectively.
> > Of cause for supercell height >100 Å the convergence in Fermi energy is
> > better but in literature I didn’t found so thick vacuum layers. Such
> > difference is not so pronounced for total energy (~2E-5 eV).
>   Does the Fermi energy also change with respect to the bands of your
> slab? The absolute values do not necesserily mean much. Especially in
> periodic systems, due to the Ewald summation, you could have a rigid
> shift of all levels when you change your supercell vectors.
>  Best regards,
>  Bálint
> --
> Dr. Bálint Aradi
> Bremen Center for Computational Materials Science, University of Bremen
> http://www.bccms.uni-bremen.de/en/~b_aradi
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