[Pw_forum] Gamma phonons in Si lattice

[Ezad Shojaee]

Hi
if we define the Si lattice as an FCC with 2-atoms per basis, we have the Gamma phonons as obtained in the example#2.  but it seems that if we define the lattice as a SC with 8-atoms per basis, we have a lot of frequencies which seems to have nothing in common with the first one. if there is no problem, what physics is behind it? did i miss something? and also the code seems to have problem with converging some of the modes in the 8-atoms per basis one(there are some negative freq's)
Thanx for any comment
 
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