[Pw_forum] RE: Pw_forum digest, Vol 1 #685 - 6 msgs

[sun jason]

about phonon calculation

>Message: 6
>Date: Wed, 6 Jul 2005 09:51:30 -0700 (PDT)
>From: Eyvaz Isaev <eyvaz_isaev at yahoo.com>
>Subject: Re: [Pw_forum] about phonon calculation
>To: pw_forum at pwscf.org
>Reply-To: pw_forum at pwscf.org
>
>Hi,
>
>In order to get correct LO mode you should calculate
>phonons using dynmat.x from /pwtools directory.

==========================================================================================

the result I presented yesterday(0.0000    0.0001    0.0001   1055.5528   
1055.5528 1274.3693) was exactly the one, which have imported the nonlinear 
term using dynmat.x

but the LO mode is also too small after recalculatetion using q2r.x + 
dynmat.x
did you get the LO mode near 1305 cm-1 ?

my input file for dynmat.x is like this:
============================================
 &input
    asr=.true.,  
    amass(1)=10.81100, 
    amass(2)=14.00674, 
    flfrc='bn111.fc', 
    flfrq='bn.freq'
 /
 9
  0.000 0.0 0.0  0.0 
  0.125 0.0 0.0  0.0  
  0.250 0.0 0.0  0.0  
  0.375 0.0 0.0  0.0  
  0.500 0.0 0.0  0.0  
  0.625 0.0 0.0  0.0  
  0.750 0.0 0.0  0.0  
  0.875 0.0 0.0  0.0  
  1.000 0.0 0.0  0.0  
=============================================

best,
jason

>Effective charges for B and N are not equal due to
>numerical errors in our computer calculations.
>
>Bests,
>Eyvaz.
>
>--- sun jason <jasonsun98 at hotmail.com> wrote:
>
> > Dear all,
> >
> > I executed a test of phonon calculation of cubic BN,
> > the input for scf is
> > like this
> >
>===========================================================================

> > &SYSTEM
> >                        ibrav = 2,
> >                     celldm(1)= 6.792,
> >                          nat = 2,
> >                         ntyp = 2,
> >                      ecutwfc = 50.0 ,
> >  /
> >  &ELECTRONS
> >                     conv_thr = 1.0d-9 ,
> >                  mixing_beta = 0.7 ,
> >  /
> > ATOMIC_SPECIES
> >     B   10.81100  B.pz-vbc.UPF
> >     N   14.00674  N.pz-vbc.UPF
> > ATOMIC_POSITIONS
> >     B      0.000000000    0.000000000    0.000000000
> >
> >     N      0.250000000    0.250000000    0.250000000
> >
> > K_POINTS automatic
> >   6 6 6   1 1 1
> >
>===========================================================================

> >
> > and the result of dielectric tensor and effective
> > charge is like this:
> >
> >
>===========================================================================

> > Dielectric constant in cartesian axis
> >
> >           (       4.637335813       0.000000000
> >  0.000000000 )
> >           (       0.000000000       4.637335813
> >  0.000000000 )
> >           (       0.000000000       0.000000000
> >  4.637335813 )
> >
> >           Effective charges E-U in cartesian axis
> >
> >            atom      1
> >           (        1.85986        0.00000
> > 0.00000 )
> >           (        0.00000        1.85986
> > 0.00000 )
> >           (        0.00000        0.00000
> > 1.85986 )
> >            atom      2
> >           (       -1.82935        0.00000
> > 0.00000 )
> >           (        0.00000       -1.82935
> > 0.00000 )
> >           (        0.00000        0.00000
> > -1.82935 )
> >
> >
>===========================================================================

> > and the frequency at gamma point is like this:
> >
>===========================================================================

> > 0.0000    0.0001    0.0001 1055.5528 1055.5528
> > 1274.3693
> >
>===========================================================================

> >
> > so my question is:
> >
> > 1)why the LO mode is so small(the exact value is
> > about 1305 cm-1) when the
> > TO mode is correct? and how to improve it?
> >
> > 2) why the absolute value of effective charge for B
> > atom and N atom is not
> > equal?
> >
> > any help would be appreciate much!
> >
> >
> > jason
> >
> >
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
> >
>
>
>
>
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