[QE-users] About the Question on pw forum negative frequency suoercell

[Fabio Costa]

Dear Ghadiyali

Thank you for your reply. I know it is a rather high doping level, but it is intentional. I understand that with such a high value it is possible that the whole thing is unstable.

My doubt is wether these strange results are due to an instability or due to some convergence issue.

I performed another test, with the same system, but now with a bigger cell, leading to a doping concentration of 6.25%, obtaining a similar result, with three completely negative optical modes.

To me, the main question here is to understand wether these results are due to a real instability, or this may be because of some mistake I did.

Thank you for your attention
Fábio Costa
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