[Pw_forum] phonon dispersion

xirainbow nkxirainbow at gmail.com
Thu Nov 12 08:04:19 CET 2009

Dear Mehrnaz  :

2009/11/12 Mehrnaz Anvari <anvari_meh at physics.iust.ac.ir>

> Hi
> You said that if this problem(non zero acoustic frequency at gamma
> point ) appears even after choosing asr option, it relates to  numerical
> noise.
Now which order of this noise is acceptable?
I think it is up to you.

In the periodic calculation, the two rotational mode never really
vanish due to weak interaction with the periodic images of the

Even using Gaussian03, which does not use period boundary condition,
the rotational frequency never equals to zero.

There is an example of Hydrogen molecule. You can find it in PW_forum:


Hui Wang
School of physics, Nankai University, Tianjin, China
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