[Pw_forum] phonon dispersion curve

[Stefano de Gironcoli]

In any system with nat atoms per unit cell  there are 3*nat frequencies 
at any q-vector in the BZ since there are 3*nat independent 
displacements that can be performed.
stefano

zahra sadat naghavi wrote:
> dear anybody!
> with zonefolding approximation there must be 6*(n+1)  branches in 
> phonon dispersion curve for achiral  nanotubes , for (6,6)  it becomes 
> 42, but i found  45 frequencies at G.
> what is the wrong?
>
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