[Pw_forum] supercell in matdyn.x

[babr aram]

Dear all, I would like to use matdyn.x to calculatephonon dos but i don't know the difference between 
(1): making a 2*2*2 supercell and running ph.x calculation for supercell and then running matdyn.x to calculte phonon dos
 and
(2):  running ph.x calculation for unit cell (or primitive cell) and then matdyn.x for supercell (for l1=2, l2=2, l3=2).(first needs more time and second is very fast)
what is  the difference between them?

thanks a lot

babraram
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