[Pw_forum] phonon at Gamma point

[lan haiping]

Dear Yansun

Thank you !
Since i just use  experimental  values of the lattices,
i didnot  optimize the lattices and just relaxed the internal coordinates.
 Should I optimize the lattices using "vc-relax" , and then run the
ph.xcalculation again ?

Regards,

Hai-Ping



On 8/20/06, Yansun Yao <yay451 at mail.usask.ca> wrote:
>
> Dear Haiping,
>
>      Other than the internal coordinates, did you optimize the unit cell?
>
>      Cheers
>                                            Yansun
>
>
> Quoting lan haiping <lanhaiping at gmail.com>:
>
> > Dear All,
> > I also have calculated gamma phonon frequencies of anatase TiO2 .
> > I run ph.x caculation after relaxing the structure, but  9 of 18
> frequencies
> > are minus.
> >
> > Would you please give me some hints and help?
> >
> > input settings are below, thank you in advance !
> >
> > *phonons of TiO2 at Gamma
> >  &inputph
> >   tr2_ph=1.0d-14,
> >   recover=.true.,
> >   epsil=.true.,
> >   prefix='tio2',
> >   fildyn='TiO2-gamma.dyn',
> >   outdir='/home/haiping/tmp/'
> >  /
> > 0.0 0.0 0.0*
> > **
> > *Relaxing calculation input :*
> > *&CONTROL
> >              title = 'TiO2' ,
> >        calculation = 'relax',
> >          verbosity = 'default',
> >            tprnfor = .true.,
> >             outdir = '/home/haiping/tmp/',
> >             prefix = 'tio2',
> >            disk_io = 'default',
> >              nstep = 200,
> >         pseudo_dir = '/home/haiping/espresso/pseudo/',
> > /
> > &SYSTEM
> >                 ibrav= 14,
> >                celldm(1)=10.2856,celldm(2)=1.0,celldm(3)=1.0,
> >                celldm(4)=-0.759357,celldm(5)=-0.759357,
> >                celldm(6)=0.518714
> >                nat = 6 ,
> >               ntyp = 2 ,
> >               nbnd = 30 ,
> >            ecutwfc = 30.0000000000,
> >            ecutrho = 160.000,
> >        occupations = 'fixed' ,
> > /
> >
> >
> > &ELECTRONS
> >   electron_maxstep = 100,
> >           conv_thr = 1.0e-07,
> >        mixing_mode = 'plain' ,
> >        startingpot = 'atomic' ,
> >        startingwfc = 'atomic' ,
> >        mixing_beta = 0.300000000,
> >        mixing_ndim = 8,
> >    diagonalization = 'david_overlap' ,
> >   diago_david_ndim = 8,
> > /
> >
> > &IONS
> >              ion_dynamics = 'bfgs',
> >              pot_extrapolation = 'first_order',
> >              wfc_extrapolation = 'first_order',
> >
> > /
> >
> > ATOMIC_SPECIES
> > O  15.999 O.pw91-van_ak.UPF
> > Ti 47.867  Ti.pw91-nsp-van.UPF
> > ATOMIC_POSITIONS crystal
> > Ti    0.00000   0.00000   0.00000
> > Ti    0.75000   0.25000   0.50000
> > O     0.20800   0.20800  -0.00000
> > O     0.95800   0.45800   0.50000
> > O     0.54200   0.04200   0.50000
> > O     0.79200   0.79200  -0.00000
> > K_POINTS   automatic
> > 6 6 7   0 0 0
> >
> > *
> >
> >
> > On 8/19/06, Ezad Shojaee <ezadshojaee at hotmail.com> wrote:
> > >
> > > hi
> > > i am trying to calculate phonon frequencies at gamma point of
> > > TiO2(anatase)
> > > and i have relaxed the structure enough (i think )but performing
> PH.Xafter
> > > scf, 2of 18 frequencies  are minus!
> > > i want to know that what technical problem do i have? does anyone
> > > calculate
> > > these beore?
> > > any suggestion will be appreciated
> > >
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>
>
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