[Pw_forum] weird phonon frequencies for 3X 3X 1 KPOINTS

[Mehmet Topsakal]

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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