Dear all, I am trying to calculate phonon dispersion. Firstly, I try to run phonon calculation at gamma point and use dynmat.x to get the vibration frequency at gamma. It imposed well frequencies with zero for 3 acoustic modes.
After that, I try to calculation phonon using grid and calculate force by q2r.x. The phonon dispersion was calculated by matdyn.x. However, I got a negative value of acoustic modes at gamma point. The value is around -20cm-1. I have used asr=simple for all calculations. Could you please give me some hints to overcome this issue? It seems negative value originated from numerical error (dynmat.x imposed well zero frequency) but I can not understand why they imposed negative values by matdyn.x. I would like to thank for all your instructions. Best regards, ----------------------------------------------- Dinh Loc Duong , Ph.D Postdoctoral Researcher, Department of Nanoscience Max Planck Institute for Solid State Research Heisenbergstrasse 1, D-70569 Stuttgart, Germany Email: [email protected], [email protected]
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