[Pw_forum] Acoustic branches

[degironc]

close to gamma the acoustic branches have linear dispersion.
Away from gamma one should follow the modes that are connected
to these three modes at gamma. If there is no symmetry these are just
the three lowest branches. If there is some symmetry they can cross
a few branches with different symmetry labels and should be possible
to follow the acoustic ones comparing the eigenvectors.
But I dont see any special meaning of acoustic modes far away from
gamma.
What are you looking for ?

stefano

meheut at impmc.jussieu.fr wrote:

> Dear Drs,
>
> I would like to use pwscf to compute the acoustic branches only of the
> crystal. I already computed the complete phonon dispersion, but the
> acoustic branches are crossing with other modes. Do you think possible
> to disjoin the acoustic modes frequencies from the other modes?
>
> Best wishes.
>
> Merlin meheut
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