[Pw_forum] Question about the PHonon example 15 calculation

[Yi-Ping Huang]

Hi,

I just recently install quantum espresso5.1.1. So I am pretty new to the
use of PHonon. When I start to run example 15, the Raman signal of CO2, I
got the bending mode split into two different peaks. That confuses me. I
though the two bending modes should be degenerate since the system should
have axial symmetry along the O=C=O axis. And I check the reference, it
seems the reference also got the double peaks. From symmetry point of view,
if the system did not break the axial symmetry the two modes should be
degenerated. Why it is so?

Thanks.
Best,
Yi-Ping
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