[QE-users] Different phonon frequencies at Gamma point via q2r.x + dynmat.x and matdyn.x calculation.

[zhishuohuang at gmail.com]

Dear all,

 

I encountered one problem when doing phonon calculations. 

 

I tried to do the test calculation provided in the
'qe-6.8/PHonon/examples/GRID_example'. 

After the whole calculations finished, the phonon frequencies of Gamma point
are shown below:

###################################################

&plot nbnd=   6, nks= 161 /

            0.000000  0.000000  0.000000

   -0.0000   -0.0000   -0.0000  375.5206  375.5206  410.5615

.

.

###################################################

 

The input file is 

###################################################

&input

  asr='simple',

  flfrc='AlAs.fc',

  flfrq='AlAs.freq',

  flvec='AlAs.modes',

  q_in_band_form=.true.,

  amass(1)=26.98,

  amass(2)=74.92,

/

6

  0.000 0.0 0.0   40

  1.0   0.0 0.0   20

  1.0   0.5 0.0   20

  1.0   1.0 0.0   40

  0.00  0.0 0.0   40

  0.5   0.5 0.5    1

###################################################

 

 

However, if I used the first dynamic matrix, which corresponds to that of
Gamma point, and do phonon calculation for Gamma point via dynmat.x with the
input file:

###################################################

&input

fildyn='AlAs.dynG', asr='simple',

fileig='AlAs.eigfile', filout='AlAs.normal'

amass(1)=26.98,

amass(2)=74.92,

/

###################################################

 

The output file is 

###################################################

     Program DYNMAT v.6.8 starts on  3Feb2022 at 16:54:12

 

     This program is part of the open-source Quantum ESPRESSO suite

     for quantum simulation of materials; please cite

         "P. Giannozzi et al., J. Phys.:Condens. Matter 21 395502 (2009);

         "P. Giannozzi et al., J. Phys.:Condens. Matter 29 465901 (2017);

         "P. Giannozzi et al., J. Chem. Phys. 152 154105 (2020);

          URL http://www.quantum-espresso.org",

     in publications or presentations arising from this work. More details
at

     http://www.quantum-espresso.org/quote

 

     Parallel version (MPI & OpenMP), running on       4 processor cores

     Number of MPI processes:                 4

     Threads/MPI process:                     1

 

     MPI processes distributed on     1 nodes

     R & G space division:  proc/nbgrp/npool/nimage =       4

     121728 MiB available memory on the printing compute node when the
environment starts

 

 

     Reading Dynamical Matrix from file AlAs.dynG

     ...Force constants read

     ...epsilon and Z* read

     A direction for q was not specified:TO-LO splitting will be absent

 

     Polarizability (A^3 units)

     multiply by 0.190550 for Clausius-Mossotti correction

        43.491364    0.000000   -0.000000

         0.000000   43.491364    0.000000

        -0.000000    0.000000   43.491364

 

     IR activities are in (D/A)^2/amu units

 

# mode   [cm-1]    [THz]      IR

    1     -0.00   -0.0000    0.0000

    2      0.00    0.0000    0.0000

    3      0.00    0.0000    0.0000

    4    375.52   11.2578    7.6122

    5    375.52   11.2578    7.6122

    6    375.52   11.2578    7.6122

 

     DYNMAT       :      0.01s CPU      0.03s WALL

 

 

   This run was terminated on:  16:54:12   3Feb2022

 

=---------------------------------------------------------------------------
---=

   JOB DONE.

=---------------------------------------------------------------------------
---=

###################################################

 

The highest phonon frequencies (375.52 cm $^{-1}$ vs 410.5615 cm $^{-1}$)
differ a lot. 

 

Could anyone please tell me why there is such a hug difference? And how to
eliminate the difference?

 

I also tried calculations on other materials, the single point phonon
calculation at Gamma point gives no imaginary frequencies while when doing
the full phonon dispersion calculations, there exist huge imaginary
frequencies at Gamma point. 

 

Best regards

Zhishuo Huang

 

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