# [Pw_forum] About the Frozen Phonon Method

Mon Aug 1 16:56:13 CEST 2011

```Dear Prof. Baroni

I wonder shouldn't the plot show the same frequency for a range of
displacements? And the same freq. for the range to be the harmonic
frequency? or the zero displacement limit, is the harmonic frequency?
And when I test the displacements with the same amplitude, but different in
sign (regarding the inward and outward atomic movements in the basis) I do
not get the same results. Shouldn't the plot have symmetry vs. the vertical
axis?

Thank You again

On Mon, Aug 1, 2011 at 6:33 PM, Stefano Baroni <baroni at sissa.it> wrote:

> Hi Mohaddesh. I do not understand why you say that the calculated frequency
> (which, I assume you define as 2 * Delta E / u^2 ???) does not converge as
> u->0. According to your plot, it does, and to a reasonable value. The finite
> slope of your plot around u=0 seems to me nothing but a manifestation of
> cubic anharmonicity ... What's wrong in this? SB
>
>
>
> Dear users,
>
> I have plotted the harmonic frequency (obtained within the frozen phonon
> approach) of Diamond as a function of atomic displacements (small
> displacements in the [1 1 1] direction, u(1)=±(u,u,u) and
> u(2)=±(-u,-u,-u) are the displacements of two atoms in the basis). I expect
> to see a range of displacements that tend to the similar frequency, but
> there is no convergence in the plot. Also, the displacements with the same
> amplitude but different in sign, do not tend to the same frequency, which is
> not what I expect, too. The plot is attached.
> I was wondering if anyone could help me to find the source of error. I
> should expect the mentioned symmetry, right? Why there is no convergence?
>
>
> Yours,
> ---------------------------------------------------------
>
> Room No. 323, Department of Physics,
> University of Tehran, North Karegar Ave.,
> Tehran, P.O. Box: 14395-547- IRAN
> Website:  http://physics.ut.ac.ir
>
> ---------------------------------------------------------
>
> <fig..pdf>_______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>
>  ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
> http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) /
> stefanobaroni (skype)
>
> La morale est une logique de l'action comme la logique est une morale de la
> pensée - Jean Piaget
>
> Please, if possible, don't  send me MS Word or PowerPoint attachments
> Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html
>
>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>

--
---------------------------------------------------------

Room No. 323, Department of Physics,
University of Tehran, North Karegar Ave.,
Tehran, P.O. Box: 14395-547- IRAN
Tel. No.: +98 21 6111 8634  & Fax No.: +98 21 8800 4781
Cellphone: +98 917 731 7514
Website:  http://physics.ut.ac.ir

---------------------------------------------------------
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20110801/d123df66/attachment.html>
```