[Pw_forum] metallic or not

Eyvaz Isaev eyvaz_isaev at yahoo.com
Tue Apr 18 22:07:08 CEST 2006

Hi Sergei,

One can suggest that it is due to the LDA which
underestmate the band gap. Did you check with a
pseudopotential you used the band gap in Si, and
unrelaxed clathrate? Is your clathrate direct or
indirect semiconductor?

On the other side relaxation will violate  your
initial symmetry that may lead to appearence
additional bands so that a band cross-section might
take place.
Please pay attention that you may have a direct band
gap for a given k-point (even a set of k-points) in
BZ, but indirect gap might be close to zero.
In this case  according DOS calculations you can not
conclude whether you have metal or semoconductor. In
this case band structure calculations are more useful.

Hope it helps,

--- Sergey Lisenkov <proffess at yandex.ru> wrote:

>  Dear all,
>   I have a problem. I am stdying the silicon
> clathrates. One of them has became metallic after
> full relaxation using pwscf (2.1.5 version). It is
> well known that silicon clathrates have band gap
> wider than tetrahedral silicon.
>  What can be the problem?
>   Thanks,
>    Sergey
> _______________________________________________
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