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<div class="moz-cite-prefix">in polar materials the long range
nature of Coulomb interaction makes the dynamical matrix non
analytical in the q->0 limit. This originates the so called
LO-TO splitting.<br>
In cubic semiconductors this splitting is such that the LO
frequency is direction independent but in systems of low enough
symmetry the dielectric response and the effective charges tensors
are not simply multiples of the identity. Hence the LO (and TO)
frequencies may depend on the <br>
direction of approach to the gamma point.<br>
<br>
see for instance the phonon dispersion in wurtzite semiconductors<br>
<br>
Bungaro and de Gironcoli, "Ab initio study of phonons in wurtzite
AlxGa1-xN alloys", Applied Physics Letters 76, 2101-2103
(2000),DOI: 10.1063/1.126268<br>
<br>
stefano<br>
<br>
<br>
On 27/04/2016 14:29, Atanu Paul wrote:<br>
</div>
<blockquote
cite="mid:CAE4rxGepZ+jfDrK6sAsBv=303O5Wav21K5+81GTgCz63kwd2xw@mail.gmail.com"
type="cite">
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<div>Hello all,<br>
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?<br>
<br>
</div>
Thanking you in advance. <br>
<br>
</div>
atanu<br>
</div>
<br>
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