[Pw_forum] phonon at Gamma point

[lan haiping]

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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