[Pw_forum] phonon at Gamma point

[Yansun Yao]

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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>