[QE-users] phonon dispersion

[Paolo Giannozzi]

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
> 
> 
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216