[Pw_forum] Using dynmat.x or not - H trapped in a rigid W vacancy

[Nicolas Fernandez]

Dear all,

I am working on hydrogen trapping in a tungsten vacancy.
* I first create a vacancy in a 3x3x3 supercell that I optimize,
* Then I trap a H atom inside, then I relax the system,
* I further need to know the phonon frequencies of the hydrogen atom to
compute thermodynamic properties.
Due to the mass difference between H and W, the phonon modes associated to H
are assumed to be decoupled from the W ones. So the only H phonon modes are
calculated at the gamma point.

My question is about dynmat.x. Should I use it or not ?

As recommended in the phonon tutorial file
(http://www.quantum-espresso.org/wp-content/uploads/2013/06/phonons_tutorial
_shanghai1.pdf) I run dynmat.x routine after the phonon calculation.

Dynamt.x is designed to impose the acoustic sum rule to the acoustic modes.
But in my case there are no acoustic modes since all the W atoms are fixed.
The problem is that H frequencies look like very different with and without
dynmat.x.

So my question, what are the correct ones ?

I attach below:
The inputs w3_vac_HOh_ph.in  w3_vac_HOh_dynmat.in and outputs
w3_vac_HOh_ph.out, w3_vac_HOh_dynmat.out of the phonon calculation.


Many thank you for your help

====================================================================
Nicolas Fernandez, PhD student
Equipe de Spectrométrie et Dynamique Moléculaire
Laboratoire de Physique des Interaction Ioniques et Moléculaire (PIIM)
UMR-CNRS 7345, Aix Marseille Université
Campus de St Jérôme, Service 252
13397 Marseille Cedex 20



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