[Pw_forum] negative frequency in high q-mesh

[Suza W]

Dear Dr. Wei-Bing Zhang,

The curves show unstable phonon at and near q = 0.19 .
You can compute phonon explicitly at q = 0.19 using QE
by giving one q point specifically instead of computing nq = NxNxN .
This will avoid any artifact which may arise from the interpolation method
used.
After all careful checking, if you find that the phonon is indeed
imaginary, then
the comment of Prof. Paolo Giannozzi is correct. No one can be sure
that  silicene is mechanically stable, unless there is any experimental
proof.

Cheers !!!!
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