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<p>Hello,</p>
<p>to add a bit on Paolo's answer, as this is quite a common
problem. If your materials is metallic or almost metallic at the
DFT level that you are using, you have to treat it as such when
doing a phonon calculation, or the dielectric response will not
converge to a meaningful result, and give bad dielectric matrix
and/or effective charges.<br>
</p>
<p>In particular, in your case, InN is a bad metal in PBE, i.e. it
has a "negative gap" with a pocket of electrons. This pocket may
give random results depending on the number of k-point, you
definitely cannot ignore it. The fact that you compute a
Dielectric tensor of >54'000 should have alerted you that
something non-physical was going on (the code could also issue a
warning for such large value, but then there are highly
polarizable materials with very large epsilon).<br>
</p>
<p>If you really need it to be an insulator, you need to find a way
to open the gap.<br>
</p>
<p>hth<br>
</p>
<p>p.s. I'm not sure exactly why this breaks the phonon
calculation, there is a sum whose cutoff that depends on the
average value of epsilon, which may not be a great choice when it
is so anisotropic.</p>
<p><br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 05/06/2025 16:57, Paolo Giannozzi
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:99d55bdd-1246-436e-b42b-73caea4bb250@uniud.it">Hi
<br>
<br>
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).
<br>
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.
<br>
<br>
Thanks to Pietro Delugas and Lorenzo Paulatto for help on this
subject.
<br>
<br>
Paolo
<br>
<br>
On 01/06/2025 01:07, Ivan Dario Arellano Ramirez wrote:
<br>
<blockquote type="cite">
<br>
Hi QE users
<br>
<br>
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.
<br>
<br>
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.
<br>
<br>
Could anyone help me understand the origin of these two issues:
<br>
1) in the top figure, v.6.4.1 the anomalous U-shape of one of
the acoustic branches near the gamma point.
<br>
2) In v. 7.3, the oscillations around the gamma and A points.
<br>
<br>
Any insights or suggestions would be appreciated
<br>
<br>
Here are the ph.in <a class="moz-txt-link-rfc2396E" href="http://ph.in"><http://ph.in></a>, q2r.in
<a class="moz-txt-link-rfc2396E" href="http://q2r.in"><http://q2r.in></a>, matdyn.in <a class="moz-txt-link-rfc2396E" href="http://matdyn.in"><http://matdyn.in></a>
<br>
<br>
Phonons of InN at G!=0
<br>
&inputph
<br>
tr2_ph = 1.0d-14,
<br>
ldisp = .true.,
<br>
search_sym = .false.,
<br>
prefix = 'inn-ph',
<br>
recover = .true.
<br>
fildyn = 'inn-ph.dyn',
<br>
nq1 = 5,
<br>
nq2 = 5,
<br>
nq3 = 3,
<br>
amass(1) = 114.818,
<br>
amass(2) = 14.007,
<br>
outdir = './tmp'
<br>
/
<br>
<br>
&INPUT
<br>
fildyn = 'inn-ph.dyn',
<br>
zasr = 'crystal'
<br>
flfrc = 'inn-ph.fc'
<br>
/
<br>
<br>
&input
<br>
asr = 'crystal',
<br>
flfrc = 'inn-ph.fc',
<br>
flfrq = 'inn.band.freq'
<br>
flvec = 'inn.band.modes'
<br>
amass(1) = 114.818,
<br>
amass(2) = 14.007,
<br>
q_in_band_form = .true.
<br>
/
<br>
8
<br>
0.0000000000 0.0000000000 0.0000000000 40 ! Gamma
<br>
0.5000000000 0.0000000000 0.0000000000 25 ! M
<br>
0.3333333333 0.3333333333 0.0000000000 40 ! K
<br>
0.0000000000 0.0000000000 0.0000000000 25 ! Gamma
<br>
0.0000000000 0.0000000000 0.5000000000 40 ! A
<br>
0.5000000000 0.0000000000 0.5000000000 25 ! L
<br>
0.3333333333 0.3333333333 0.5000000000 40 ! H
<br>
0.0000000000 0.0000000000 0.5000000000 1 ! A
<br>
<br>
Regards,
<br>
<br>
-- <br>
<br>
Iván Darío Arellano Ramírez
<br>
<br>
Profesor Titular Programa de Ingeniería Física
<br>
<br>
Director Grupo de Investigación en Modelado y Simulación
Computacional
<br>
<br>
Universidad Tecnológica de Pereira
<br>
<br>
<br>
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</blockquote>
<br>
</blockquote>
<div class="moz-signature">-- <br>
<small>Dr. Lorenzo Paulatto<br>
IR IMPMC - CNRS UMR 7590 / Sorbonne Université / MNHN <br>
phone: +33 (0)1 442 79822 / telegram: lpaulatto<br>
<a href="http://www.impmc.upmc.fr/~paulatto/"
class="moz-txt-link-freetext">http://www.impmc.upmc.fr/~paulatto/</a>
- <a href="https://anharmonic.github.io/"
class="moz-txt-link-freetext">https://anharmonic.github.io/</a><br>
23-24/423 B115, 4 place Jussieu 75252 Paris CX 05<small></small></small></div>
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