[Pw_forum] negative frequency

[xirainbow]

Dear P S Ghosh：

Do you relax the crystal ?
Firstly, relax crystal with "*calculation = 'vc-relax' *".
Phonon should be calculated after  vc-relax,

On Wed, May 19, 2010 at 8:11 PM, partha sarathi ghosh <
parthasarathi13 at gmail.com> wrote:

> Dear all,
>              I am trying to do phonon calculation of bcc-Zr from (0,0,0) to
> (1,1,1) in q-space.But I am getting negative frequencies in several
> q-points, also my curve is very different from experimental one. I optimized
> the system w.r.t ecutwf, ecutrho ,conv_thr, k-point sampling .I also tried
> the same calculation by changing potential also.I am new fellow in this
> field so I am unable to understand what is happening wrong !!
> My input files are :
> 1) zr.scf.in
>  &control
>     calculation='scf'
>     restart_mode='from_scratch',
>     tstress = .true.
>     tprnfor = .true.
>     prefix='zr',
>     pseudo_dir = '/home/general/Desktop/espresso-4.0.5/pseudo/',
>     outdir='./'
>  /
>  &system
>     ibrav=  0, celldm(1) =6.7, nat=  1, ntyp= 1,
>     degauss=0.04,
>     smearing='mp',
>     occupations='smearing',
>     ecutwfc =35.0
>     ecutrho = 350.0
>  /
>  &electrons
>     conv_thr =  1.0d-8
>     mixing_beta = 0.7
>  /
> ATOMIC_SPECIES
>  Zr  91.22  Zr.pbe-nsp-van.UPF
> ATOMIC_POSITIONS
> Zr 0.00 0.00 0.00
> K_POINTS  AUTOMATIC
>  16 16 16  0 0 0
> CELL_PARAMETERS { cubic }
>   -0.500000000000000   0.500000000000000   0.500000000000000
>    0.500000000000000  -0.500000000000000   0.500000000000000
>    0.500000000000000   0.500000000000000  -0.500000000000000
>  ##########################################
> 2) zr.ph.in
> phonons of Zr
>  &inputph
>   tr2_ph=1.0d-10,
>   prefix='zr',
>   ldisp=.true.,
>   nq1=8, nq2=8, nq3=8
>   amass(1)=91.22,
>   outdir='./',
>   fildyn='zr.dyn',
>  /
> Any one can help me please .
> Thanks in advance.
> P S Ghosh
> B.A.R.C.
> India
>
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>


-- 
____________________________________
Hui Wang
School of physics, Nankai University, Tianjin, China
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