[Pw_forum] strange results in phonon calculation

Lorenzo Paulatto paulatto at sissa.it
Tue Apr 7 12:16:33 CEST 2009

On Tue, 07 Apr 2009 12:00:18 +0200, Reza Ebraahimi <rezaebraahimi at yahoo.com> wrote:

> Hi
> Trying to run phonon calculation at Gamma point for my case, the code  
> gives the following result for some of the modes:     
>      omega( 1) =*************** [THz] =*************** [cm-1]
>      omega( 2) =*************** [THz] =*************** [cm-1]
>      omega( 3) =*************** [THz] =*************** [cm-1]
> What does these mean? How should i fix this?

Dear Reza,
it means that the computed frequencies cannot fit in the output format used to print them.
As the format is quite generous (15 characters for a 6 decimal places fixed-point number) it means that your frequencies are larger or equal than 10^9 THz or negative and smaller or equal than 10^8 THz (the minus counts as one character).
In other words, it means that your scf calculation was already wrong in the first place, e.g. not enough converged or not properly relaxed and is giving you some non-realistic frequencies. It may also be some code bug, but it is less likely.

Please provide more detail¹ if you want a more insightful explanation of your problem.


[1] inputs and outputs of the scf and phonon calculations

Lorenzo Paulatto
phone: +39 040 3787 511
skype: paulatz
www:   http://people.sissa.it/~paulatto/

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