[Pw_forum] ph - computational errors in vicinity of gamma point

[Kvasov Alexander]

Dear developers,

I study flexoelectric effect which can be seen as a repulsion of TA and TO branches in the vicinity of gamma point. I calculate phonon dispersion of cubic SrTiO3. It's essential for me to have adequate picture of phonons in the vicinity of gamma point (at least for q>0.05).

The picture shows TA and TO branches single q-point (st.ph.single.in) calculations (grey dots) and dispersion (st.ph.disp.in) for 8x8x8 mesh.
[cid:image003.png at 01CFBBD0.39A26750]

With used parameters ph.x fails to give right values for small values of q-vector. I guess it's due to numerical errors of the code.
What are the main reasons for this numerical error when we go close to gamma point. Which parameters should I adjust to improve the situation?

Attached, all relevant inputs and outputs

Sincerely yours,

Alexander Kvasov
Ceramics Laboratory /  THEOS (Theory and Simulation of Materials) Laboratory
École Polytechnique Fédérale de Lausanne (EPFL)

Phone: +41 21 693 5805

Address:
EPFL STI IMX LC
MXD 220 (Bâtiment MXD) Station 12
1015 Lausanne, Switzerland

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