[Pw_forum] use of maxirr in phonon calculation

[Stefano de Gironcoli]

please note that irreducible representation is a different concept
than phonon modes.
an irreducible representation of dimension D corresponds ti D
phonon modes.
Moreover the irreducible representations are used to build the
dynamical matrix but to get the frequencies you need to diagonalize
the entire matrix. Thus computing only a subset of them IS NOT an
option for your case.
The only usefullness of maxirr is that it allows you to split the 
calculation of the matrix in several jobs but you need in any case to 
compute the full dynamical matrix to get the frequencies.

stefano

On Fri, 8 Apr 2005, Eduardo Ariel Menendez P wrote:

>
> Hello,
> I am making a phonon test calculation  and I set the parameter
> maxirr=5, just to investigate the convergence of the accustic modes with
> the cutoffs. Calculating all the modes takes too much time.
> However, the code does not stop in the fifth mode, and
> continues calculating the higher modes. Was is wrong with my input file?
> thans
> eduardo
>
> Input file:
>
> phonons at Gamma
> &inputph
>  tr2_ph=1.0d-12,
>  prefix='tisic',
>  epsil=.false.,
>  elph=.false.,
>  amass(1)=47.8671,
>  amass(2)=28.0855,
>  amass(3)=12.01078,
>  alpha_mix(1)=0.3,
>  outdir='/home/eariel/mypwscf/Ti3SiC2/Fonones/Fonones551/Convergencia/results/',
>  fildyn='/home/eariel/mypwscf/Ti3SiC2/Fonones/Fonones551/Convergencia/results/tisic.dynG',
>  maxirr=5
> /
> 0.0 0.0 0.0
>
>
>
> Eduardo A. Menendez Proupin
> Department of Physics
> Faculty of Science
> University of Chile
> Las Palmeras 3425
> Ñuñoa, Santiago
> Chile
> Phone: 56+2+678 74 11
> http://fisica.ciencias.uchile.cl/~emenendez/
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