[QE-users] phonon dispersion

[Ivan Dario Arellano Ramirez]

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, q2r.in, 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

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