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[Emmanuel Arras <emmanuel.arras@cea.fr>]

ok, my mistake, the phase is important. It is the actual phase applied 
on each atom of the unit cell in the collective displacements. I thought 
there could not be such a phase, but it does if there are bonds with 
different rigidity. And indeed one must be able to give informations 
about bond strenght from these phases.
(Hope that time I'm right)

Thank you for your time and sorry for this " basic " question.


Xavier Gonze a écrit :
> Dear Emmanuel,
>
> The eigenmode characterizing a phonon should always be thought as a 
> collective pattern of displacements
> describing oscillations with time. The phases (or the real and 
> imaginary components) are important, as they will describe
> the atomic displacements with a form like
>
> a_r  * cos (omega*t)   + a_i * sin (omega*t)
>
> As suggested by Nishimatsu-san, please read a basic textbook about 
> phonons (and normal modes of vibrations).
>
> Best regards,
> Xavier
>
>
> On 18 Aug 2009, at 19:54, Emmanuel Arras wrote:
>
> > Thanks for the reference,
> > As I understand it, the comlpex phase it is simply the phase 
> > associated with the fourrier transform, that is the action of q.r in 
> > the primitive cell ( D(k)=D(-k)* ). So I would say it is useless 
> > since the information is already known via q and the atomic positions.
> >
> > As for the absolute amplitude, it seems to be simply a 
> > renormalization factor taking into account the number of atoms, their 
> > mass and the frequency of the phonon.
> >
> > Thank you again.
> >
> >
> >
> > Takeshi NISHIMATSU a écrit :
> > > Emmanuel,
> > >
> > > You should read a basic textbook on solid state
> > > physics and phonon. Par exemple, CHAPTER 3 of
> > > "Theoretical Solid State Physics, Vol.1: Perfect
> > > Lattices in Equilibrium" by William Jones and
> > > Norman H. March.
> > >
> > >
> > > > when I compute phonons, for each mode, the atomique 
> > > > displacementvectors' coordinates are given
> > > > by complexe numbers (in anaddb.out,since my _PHVEC file is empty 
> > > > whatever eivec but
> > > > that'sanother problem). I get that the norm of these complexes are 
> > > > thecoordinates of the
> > > > atomique displacementvectors, but I wonder what is the meaning of 
> > > > the complexe phaseassociated.
> > > >  :
> > > Hint: D(k) and D(-k)
> > >
> > > Bonne chance,
> >
> > --
> > Emmanuel ARRAS
> > L_Sim (Laboratoire de Simulation Atomistique)
> > SP2M / INAC
> > CEA Grenoble
> > tel : 00 33 (0)4 387 86862

--
Emmanuel ARRAS
L_Sim (Laboratoire de Simulation Atomistique)
SP2M / INAC
CEA Grenoble
tel : 00 33 (0)4 387 86862