[Pw_forum] Phonon weirdness with matdyn

[Eyvaz Isaev]

Hi Miguel,

Does your sih4.dyn0 contain the macroscopic dielectric constants and Born effective charges? According to your input file it should, as your system contains 4*2+1*8=16 electrons and you did not specify occupations (so, your system is considered as semiconducting).

If this suggestion is true, then you have LO-TO splitting at the Gamma point, and there is no phonon weirdness. Contrary, it reflects the real behaviour of the material you studied.

Bests,
Eyvaz.

-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com


--- On Wed, 6/24/09, Miguel Martínez <miguel.martinez at ehu.es> wrote:

> From: Miguel Martínez <miguel.martinez at ehu.es>
> Subject: [Pw_forum] Phonon weirdness with matdyn
> To: "PWscf Forum" <pw_forum at pwscf.org>
> Date: Wednesday, June 24, 2009, 10:49 PM
> 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
> ----------------------------------------
> 
>  "If you have an apple and I have an apple and
>  we exchange these apples then you and I will
>  still each have one apple. But if you have an
>  idea and I have an idea and we exchange these
>  ideas, then each of us will have two ideas."
> 
>  George Bernard Shaw 
> 
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