[QE-users] Matdyn.x bands with negative frequency after a ph.x calculation

[Martino Napoli - martino.napoli@studio.unibo.it]

Hi everyone,
I ran a ph.x-calculation with such input:
```
&Inputph
  outdir    = './'
  prefix    = 'rutile'
  fildyn    = 'rutile.dyn'
  nq1       = 3
  nq2       = 3
  nq3       = 3
  ldisp     = .true.
  verbosity = 'high'
  tr2_ph    = 1.0d-14
  nmix_ph   = 10
/
```
and the procedure has terminated correctly, I cannot attach the output file due to its size, but the phonons calculated in each selected point are positive.
Then I ran a q2r.x calculation with this input:
```
&INPUT
prefix = 'rutile'
fildyn = 'rutile.dyn'
flfrc  = 'rutile.fc'
zasr   = 'crystal'
/
```
and lately a matdyn.x with this input:
```
&INPUT
  asr = 'crystal'
  flfrc = 'rutile.fc'
  flfrq = 'rutile.freq'
  flvec = 'rutile.modes'
  q_in_band_form = .true.
/
7

   0.0000000000     0.0000000000     0.0000000000  60    !GAMMA
   0.5000000000     0.5000000000     0.0000000000  60    !M
   0.0000000000     0.5000000000     0.0000000000  60    !X
   0.0000000000     0.0000000000     0.0000000000  60    !GAMMA
   0.0000000000     0.0000000000     0.5000000000  60    !Z
   0.0000000000     0.5000000000     0.5000000000  60    !R
   0.5000000000     0.5000000000     0.5000000000  60    !A
```
from the latter, I obtain negative (immaginary) frequency in the output, and in general the bands are all messed up, while the frequency obtained in the first ph.x step are reasonable.
Is it an error? How do I get rid of it?

Thank you in advance!
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