[Pw_forum] Gamma point frequencies are not unique in the dispersion curve

[Atanu Paul]

Hello all,
I am new to use PWscf code. I have been trying to calculate the phonon
dispersion of a 2d structure using Pwscf code. Dynamical matrices have been
calculated with 4x4x1 mesh. Then I have used 'q2r.x' and 'matdyn.x' to get
the phonon dispersion curves. The structure of the unit cell is
orthorhombic and the high symmectric kpoint path is taken as G-Y-S-X-G. Now
If I look at the dispersion curve, the frequencies at Gamma(G) point (
approaching from G-Y, i.e along y-axis in reciprocal space) is different
from the frequencies at Gamma(G) point (approaching from X-G, i.e along
x-axis in reciprocal space). How can frequency be different at Gamma point?
Though I have got positive frequency at any k-points after execution of
'matdyn.x'. Am I doing anything wrong?

Thanking you in advance.

atanu
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