[QE-users] phonon dispersion

[Paolo Giannozzi]

On 05/06/2025 16:57, Paolo Giannozzi wrote:

> I could reproduce your results with v.6.4.1, though

more exactly: I could reproduce, using the latest (development) version 
of QE, the results you obtained with QE v.6.4.1. So it is not a 
version-dependent problem, but a system-dependent one. By the way: with 
a smaller cutoff and k-point grid, all three components of the 
dielectric tensors become very large and the anomaly disappears as well!

Paolo

> 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