[Pw_forum] Phonon weirdness with matdyn

[Miguel Martínez]

Dear espresso users,

I computed a while ago the phonon DOS of Fdd2 silane (that is, face
centered orthorrombic) at around 50 GPa and kept the IFC matrix. I
wanted to have a look at the phonon branches and have noticed some
weird behaviour.

I'm trying to follow the Gamma - T - Z - Y -Gamma - Z2 path(see the
Brillouin Zone in 
http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-kv-list?gnum=43&fig=fmm2fcgr )

Amazingly, when I come back to Gamma, the frequencies have changed. And
they jump back to the "normal" levels after a step in the Gamma - Z2
line.

I've tried no, simple and crystal ASR in both the q2r conversion and
the matdyn run, always keeping the same ASR for the sake of
consistency. In any case, the "jump" is always present. Gamma will
display wrong frequencies (when compared to the frequencies directly
obtanied) every time the Gamma - Y line is followed in any direction.

I've used both quantum-espresso 4.0.2 compiled with ifort in an itanium
and a nightly "build" from q-e forge downloaded yesterday and compiled
with gfortran and run in my laptop, but that warrants no change.

¿Anybody has a clue on what may be happening here? For additional weird
points, this happens at both 34 and 50 GPa (I ran the phonon
calculation at both pressures). I fear I've done something silly, but I
just don't see it.

Thanks in advance,

Miguel

The SCF input is:
 &control
    calculation='scf'
    restart_mode='from_scratch',
    prefix='sih4',
    tstress = .true.
    tprnfor = .true.
    pseudo_dir = '/home/wmbmacam/pseudo/',
    outdir='/scratch/wmbmacam/fdd2-phon-50/'
 /
 &system
    ibrav= 10, celldm(1) = 12.2211446, celldm(2) = 1.07916784,
celldm(3) = 0.616658866, nat=10, ntyp= 2,
    ecutwfc = 45.0, ecutrho = 500.0
    nr1= 72, nr2= 72, nr3= 72
 /
 &electrons
    conv_thr = 1.0d-8
    mixing_beta = 0.7
 /
ATOMIC_SPECIES
 Si  28.0855 Si.pbe-n-van.UPF
  H   1.0079  H.pbe-van_ak.UPF
ATOMIC_POSITIONS {crystal}
Si 0.610686000000 0.389314000000 0.610686000000
Si 0.860686000000 0.639314000000 0.860686000000
H  0.444907000000 0.850471000000 0.348857000000
H  0.348857000000 0.355765000000 0.444907000000
H  0.894235000000 0.901143000000 0.399529000000
H  0.399529000000 0.805093000000 0.894235000000
H  0.385750000000 0.340750000000 0.013222000000
H  0.013222000000 0.260278000000 0.385750000000
H  0.989722000000 0.236778000000 0.909250000000
H  0.909250000000 0.864250000000 0.989722000000
K_POINTS {automatic}
 12 12 12  1 1 1


The Phonon input is:
 &inputph
  tr2_ph=1.0d-14,
  prefix='sih4',
  ldisp=.true.,
  nq1=4, nq2=4, nq3=4
  amass(1)=28.0855,
  amass(2)=1.00794,
  outdir='/scratch/wmbmacam/fdd2-phon-50/',
  fildyn='sih4.dyn',
 /

And finally the q2r input is:
 &input
   fildyn='sih4.dyn', zasr='crystal', flfrc='sih4.fc'
 /



PS: I'll happily provide an eps with the full phonon branches if
someone desires it. Or the sih4.dyn files.

-- 
----------------------------------------
Miguel Martínez Canales
   Condensed Matter Physics Dpt.
   UPV/EHU
   Faculty of Science and Technology
   Apdo. 644
   48080 Bilbao (Spain)
Fax:  +34 94 601 3500
Tlf:  +34 94 601 5326
----------------------------------------

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