[QE-users] phonon dispersion

Fri Jun 6 20:52:03 CEST 2025

Dear Paolo

Thank you for your detailed explanation

I recalculated the phonon dispersion using a smaller energy cutoff and
coarser k-point mesh, and I noticed that the anomalous oscillations around
the Gamma and A points disappeared. However, I now have a new question
regarding the dielectric tensor values.

Using QE v.6.4.1 with ecutwfc = 100 and 15x15x12 k-mesh I obtained *+725.22*
for both the xx and yy components of the dielectric tensor.
Using QE v.7.3, with the same cutoff and k-mesh, I instead obtained
*-48192.85* for both components.

Finally, using QE v.7.3,  with ecutwfc = 80 and 12x12x9  k-mesh, the values
changed to *+1102.27*.

I am trying to understand the cause of these large discrepancies,
especially the negative and extremely large values in the second case.

Any insights would be greatly appreciated.

Best regards,

El jue, 5 jun 2025 a las 9:57, Paolo Giannozzi (<paolo.giannozzi at uniud.it>)
escribió:

> Hi
>
> I don't know the reasons for the weird behavior with v.7.3. If you have
> split your calculation into partial one, that could be the reason
> (sometimes the "splitting" machinery does not work as expected).
> I could reproduce your results with v.6.4.1, though. If you look at the
> output (or dynamical matrix file) for q=0, you will notice very large
> values for the dielectric tensor along xx and yy. This indicates a
> quasi-metallic character of your system, presumably as a consequence of
> DFT shortcomings, spin-orbit interactions absence, or both. If you
> replace in the dynamical matrix files the dielectric tensor with the
> experimental one (exx = eyy = 14.4, ezz = 13.1) and re-compute the force
> constant matrices, the anomalous behaviour at q => 0 disappears.
>
> Thanks to Pietro Delugas and Lorenzo Paulatto for help on this subject.
>
> Paolo
>
> On 01/06/2025 01:07, Ivan Dario Arellano Ramirez wrote:
> >
> > Hi QE users
> >
> > Recently, I performed phonon calculations using the ph.x module
> > implemented in QE. I initially used the version 6.4.1 and obtained the
> > results shown in the attached figure (top). I noticed an
> > unusual behavior near the gamma point, one of the acoustic branches
> > exhibits a U-shaped anomaly  with some negative frequencies (small
> > values). The acoustic modes should approach the Gamma point linearly.
> >
> > After some time, I decided to repeat the calculations using identical
> > input file parameters, but on a different machine and with QE version
> > 7.3. In this version, the band structures shows oscillations around both
> > the gamma and A points.
> >
> > Could anyone help me understand the origin of these two issues:
> > 1) in the top figure, v.6.4.1 the anomalous U-shape of one of the
> > acoustic branches near the gamma point.
> > 2) In v. 7.3, the oscillations around the gamma and A points.
> >
> > Any insights or suggestions would be appreciated
> >
> > Here are the ph.in <http://ph.in>, q2r.in <http://q2r.in>, matdyn.in
> > <http://matdyn.in>
> >
> > Phonons of InN at G!=0
> > &inputph
> >   tr2_ph = 1.0d-14,
> >   ldisp = .true.,
> >   search_sym = .false.,
> >   prefix = 'inn-ph',
> >   recover = .true.
> >   fildyn = 'inn-ph.dyn',
> >   nq1 = 5,
> >   nq2 = 5,
> >   nq3 = 3,
> >   amass(1) = 114.818,
> >   amass(2) = 14.007,
> >   outdir =  './tmp'
> >   /
> >
> > &INPUT
> >   fildyn = 'inn-ph.dyn',
> >   zasr = 'crystal'
> >   flfrc =  'inn-ph.fc'
> >   /
> >
> > &input
> >   asr = 'crystal',
> >   flfrc = 'inn-ph.fc',
> >   flfrq = 'inn.band.freq'
> >   flvec = 'inn.band.modes'
> >   amass(1) = 114.818,
> >   amass(2) = 14.007,
> >   q_in_band_form = .true.
> >   /
> > 8
> >     0.0000000000     0.0000000000     0.0000000000  40  ! Gamma
> >     0.5000000000     0.0000000000     0.0000000000  25  ! M
> >     0.3333333333     0.3333333333     0.0000000000  40  ! K
> >     0.0000000000     0.0000000000     0.0000000000  25  ! Gamma
> >     0.0000000000     0.0000000000     0.5000000000  40  ! A
> >     0.5000000000     0.0000000000     0.5000000000  25  ! L
> >     0.3333333333     0.3333333333     0.5000000000  40  ! H
> >     0.0000000000     0.0000000000     0.5000000000  1   ! A
> >
> > Regards,
> >
> > --
> >
> > Iván Darío Arellano Ramírez
> >
> > Profesor Titular Programa de Ingeniería Física
> >
> > Director Grupo de Investigación en Modelado y Simulación Computacional
> >
> > Universidad Tecnológica de Pereira
> >
> >
> > El contenido de este mensaje y sus anexos son únicamente para el uso del
> > destinatario y pueden contener información  clasificada o reservada. Si
> > usted no es el destinatario intencional, absténgase de cualquier uso,
> > difusión, distribución o copia de esta comunicación.
> >
> >
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>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216
>
>

-- 

Iván Darío Arellano Ramírez

Profesor Titular Programa de Ingeniería Física

Director Grupo de Investigación en Modelado y Simulación Computacional

Universidad Tecnológica de Pereira

-- 
El contenido de este mensaje y sus anexos son únicamente para el uso del 
destinatario y pueden contener información  clasificada o reservada. Si 
usted no es el destinatario intencional, absténgase de cualquier uso, 
difusión, distribución o copia de esta comunicación.
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