[Pw_forum] question for phonon calculation

[Eyvaz Isaev]

> parameters used to generate.

Sorry, it should be "to generate a pseudopotential".

Bests,
Eyvaz.
 

--- On Tue, 4/21/09, Eyvaz Isaev <eyvaz_isaev at yahoo.com> wrote:

> From: Eyvaz Isaev <eyvaz_isaev at yahoo.com>
> Subject: Re: [Pw_forum] question for phonon calculation
> To: "PWSCF Forum" <pw_forum at pwscf.org>
> Date: Tuesday, April 21, 2009, 11:38 PM
> Hi,
> 
> > But I got the minus value at the lowest three branch.
> 
> > how to avoid the minus values 
> 
> Here you are incorrect, you got imaginary frequences.
> 
> 5 years ago I did such kind calculations for MgB2  using my
> own PBE US pseudopotentials and met no problem. As far as
> know phonons are sensitive to parameters used to generate.
> Most likely, you can ignore these frequences, as applying
> ASR will correct them.  As concerns how to apply ASR, just
> use matdyn.x in QE/PH or QE/bin (with keyword
> asr='crystal') file to generate phonon dispersion
> relations with correct acoustic modes at Gamma point. See
> example file /examples/example06.
> 
> >   tr2_ph=1.0d-25
> Looks extremly low. As 1.d-10 is default, the use of d-12
> or d-14 should be sufficient.
> 
> 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 Tue, 4/21/09, 潘登
> <panda.deng.pan at gmail.com> wrote:
> 
> > From: 潘登 <panda.deng.pan at gmail.com>
> > Subject: [Pw_forum] question for phonon calculation
> > To: "pw forum" <pw_forum at pwscf.org>
> > Date: Tuesday, April 21, 2009, 10:23 PM
> > Dear All Users,
> > 
> > I was going to calculating phonon frequency of MgB2 at
> > Gamma point.But I got
> > the minus value at the lowest three branch.
> > 
> >      q = (    0.000000000   0.000000000   0.000000000
> )
> > 
> > 
> >
> **************************************************************************
> >      omega( 1) =      -1.333147 [THz] =     -44.469304
> > [cm-1]
> >      omega( 2) =      -1.333147 [THz] =     -44.469304
> > [cm-1]
> >      omega( 3) =      -1.003834 [THz] =     -33.484515
> > [cm-1]
> >      omega( 4) =       9.706117 [THz] =     323.763351
> > [cm-1]
> >      omega( 5) =       9.706117 [THz] =     323.763351
> > [cm-1]
> >      omega( 6) =      11.666010 [THz] =     389.138778
> > [cm-1]
> >      omega( 7) =      15.807885 [THz] =     527.297796
> > [cm-1]
> >      omega( 8) =      15.807885 [THz] =     527.297796
> > [cm-1]
> >      omega( 9) =      20.623897 [THz] =     687.943739
> > [cm-1]
> > 
> >
> **************************************************************************
> > 
> > I had already relax the lattice.And below is my inputs
> for
> > scf and phonon
> > calculation.Any suggest and comments on how to avoid
> the
> > minus values was
> > appreciated.
> > 
> > scf.in
> >  &control
> >      calculation = 'scf'
> >      restart_mode='from_scratch'
> >      prefix='MgB2',
> >      pseudo_dir =
> > '//Quantum-Espresso/espresso-4.0.3/pseudo/',
> >      outdir='/tmp/'
> >  /
> >  &system
> >      ibrav=4,
> >      celldm(1)=5.8398,
> >      celldm(3)=1.1420,
> >      nat=3,
> >      ntyp=2,
> >      ecutwfc = 45.0,
> >      ecutrho = 450.0,
> >      occupations= 'smearing',
> >      degauss= 0.03,
> >      smearing= 'cold',
> >  /
> >  &electrons
> >      mixing_beta = 0.7
> >      conv_thr =  1.0d-12
> >  /
> > ATOMIC_SPECIES
> >  Mg 24.3 Mg.pw91-np-van.UPF
> >  B  10.8 B.pw91-n-van.UPF
> > ATOMIC_POSITIONS
> > Mg    0    0       0
> > B     0    0.57735 0.571
> > B     0.5  0.28868 0.571
> > K_POINTS {automatic}
> >  32 32 32 0 0 0
> > 
> > ph.in
> > 
> >  MgB2
> > &inputph
> >   amass(1)= 24.3,
> >   amass(2)= 10.8,
> >   prefix='MgB2'
> >   tr2_ph=1.0d-25,
> >   alpha_mix(1)=0.5,
> >   iverbosity=1,
> >   outdir='//tmp/',
> >  /
> > 0 0 0
> > 
> > I also wonder how to apply 'asr' to my
> > calculation.I could not find any
> > option for ph.x.
> > 
> > Have a nice day!
> > 
> > Deng Pan
> > Nanjing University
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
> 
> 
>       
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