[Pw_forum] Wrong degeneracy

[Stefano Baroni]

On Mar 2, 2005, at 2:15 PM, Shihn Lun wrote:

> Hello all,
>
> I want to perform a phonon calculation of bcc Te, but
> always get wrong phonon frequency.
>
> My phonon frequency of N point (0.0 0.0 0.5).
>      omega( 1) =       3.953933 [THz]
>      omega( 2) =       3.953933 [THz]
>      omega( 3) =       6.054814 [THz]
>
> But omega(1) and omega(2) should be different!

I do not know whether the above frequencies are correct or wrong. What 
I know for sure is that there is NOTHING wrong in the degeneracy of the 
two transverse frequencies at the (0,0,1/2) point of a cubic lattice. 
What makes you think that they should be different?

SB

>
> Could you give me some suggestions?
> Thanks in advance.
>
> Shihn Lun.
>
> ------------------------------------------
> Here is pw.x input
> &control
>    calculation='scf'
>    restart_mode='from_scratch',
>    pseudo_dir = '/home/sllee/work/Te_pwscf/',
>    outdir='/home/sllee/work/Te_pwscf/vol22/'
>    nstep = 100
>    prefix='te'
> /
> &system
>    ibrav= 3, celldm(1) = 6.67362382, nat=1, ntyp=1,
>    ecutwfc = 44, nbnd = 27,
>    occupations='smearing',
> smearing='methfessel-paxton', degauss=0.02
> /
> &electrons
>     diagonalization='cg'
>     conv_thr = 1.0e-10
>     mixing_beta = 0.7
> /
> ATOMIC_SPECIES
> Te 127.60 Te.pz-bhs.UPF
> ATOMIC_POSITIONS
> Te 0.0 0.0 0.0
> K_POINTS {automatic}
> 12 12 12 0 0 0
> --------------------------------------------
> Here is pw.x input fot nscf calculation
> &control
>    calculation='phonon'
>    restart_mode='from_scratch',
>    pseudo_dir = '/home/sllee/work/Te_pwscf/',
>    outdir='/home/sllee/work/Te_pwscf/vol22/'
>    prefix='te'
> /
> &system
>  ibrav=3, celldm(1) =6.472, nat=1, ntyp=1,
>  ecutwfc = 44.0,
>  occupations='smearing', smearing='methfessel-paxton',
> degauss=0.02
> /
> &electrons
> /
> &phonon
>    xqq(1)=0.0, xqq(2)=0.0, xqq(3)=0.5
> /
> ATOMIC_SPECIES
> Te 127.60 Te.pz-bhs.UPF
> ATOMIC_POSITIONS {crystal}
> Te 0.0 0.0 0.0
> K_POINTS {automatic}
> 12 12 12  0 0 0
>
> --------------------------------------------
> Here is ph.x input for phonon calculation
>
> phonons of te at 0.0 0.0 0.5
>  &inputph
>   tr2_ph=1.0d-18,
>   prefix='te',
>   amass(1)=127.60 ,
>   outdir='/home/sllee/work/Te_pwscf/vol22/',
>   fildyn='te.dyn',
>   fildvscf='tedv',
>  /
> 0.0,0.0,0.5
> ----------------------------------------------
>
>
>
> 	
> 		
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---
Stefano Baroni    ---  SISSA  &  DEMOCRITOS National Simulation Center
via Beirut 2-4 34014 Trieste Grignano / [+39] 040 3787 406 (tel) -528 
(fax)

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