[Pw_forum] [SOLVED ?] Re: weird phonon frequencies for 3X 3X 1 KPOINTS

[Mehmet Topsakal]

Dear Gabriele,

Thank you very much for your suggestion. After including some smearing,
-5000 frequencies disappeared. But this
still cannot explain the 3X 3X 1 situation. For this reason, I plotted the
positions of scf KPOINTS (see the attachments)
and realized that the corner of the Brillouin zone, which is also known as
K-special-point, is NOT included for KPOINTS
other than 3X 3X 1. For graphene, K-special-point also corresponds to the
Dirac-Point where zero-band-gap occurs.
As a result, problem should be related with K-special-point.

BUT. Still I cannot understand why inclusion of a point in BZ corresponds to
such a HUGE difference in phonon frequencies.
Maybe someone in this list gives a better explanation for that....

All of the files are available at http://db.tt/xK2Jtu1

Ragards.


On Thu, Sep 30, 2010 at 4:47 PM, Gabriele Sclauzero <sclauzer at sissa.it>wrote:

>  Dear Mehmet,
>
>    graphene has zero gap, hence you probably need to include smearing of
> the occupations in the scf calculations.
>
>
> HTH
>
> GS
>
>
> On 09/29/2010 04:54 PM, Mehmet Topsakal wrote:
>
> Dear all,
>
>  For graphene structure, I noticed that I get completely wrong phonon
> frequencies when I use KPOINTS such as 9 9 1, 12 12 1, 15 15 1
>
>  For example:
>
>  K_POINTS {automatic}
> 11 11 1    0 0 0
>
>  gives realistic frequencies as in 11.phonon.out file
>
>  BUT
>
>  K_POINTS {automatic}
> 12 12 1    0 0 0
>
>  gives "omega( 1) =    -149.592762 [THz] =   -4989.910586 [cm-1]" as
> in 12.phonon.out
>
>
>  What should be the reason ????
>
>  Thanks.
>
>  --
>
> Mehmet Topsakal  (Ph.D. Student)
> UNAM-Institute of Materials Science and Nanotechnology.
> Bilkent University. 06800 Bilkent, Ankara/Türkiye
> Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365
> UNAM-web  : www.nano.org.tr
>
>
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>
>
>
> --
>
> Gabriele Sclauzero, EPFL SB ITP CSEA
> PH H2 462, Station 3, CH-1015 Lausanne
>
>
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>


-- 

Mehmet Topsakal  (Ph.D. Student)
UNAM-Institute of Materials Science and Nanotechnology.
Bilkent University. 06800 Bilkent, Ankara/Türkiye
Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365
UNAM-web  : www.nano.org.tr
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