[Pw_forum] Convergence of imaginary modes

[Brad Malone]

Dear Nicola,

Thanks so much for your suggestion; I was not aware of this characteristic
of Kohn anomalies. I will look into some of those papers (a quick glance at
them already suggests that they may be useful). My smearing is pretty
"standard" for metallic systems at 0.03 Ry, and so I will look into the
possible presence of a Kohn anomaly in the system.

Best,
Brad
UC Berkeley


> Dear Brad,
>
>
> if you have a Kohn anomaly it's not unusual to require that high
> of a k-point sampling - comparable numbers are needed to converge
> some of the optical modes in graphene/graphite (do check some of
> the early papers of Mauri/Lazzeri).
>
> I haven't heard of other cases where such high-sampling is needed
> for phonons, unless your system was a metal, and you were not using
> a smearing scheme (or way too small a smearing).
>
>                        nicola
>
>
> --
> ----------------------------------------------------------------------
> Prof Nicola Marzari    Department of Materials    University of Oxford
> Chair of Materials Modelling  Director, Materials Modelling Laboratory
> nicola.marzari at materials.ox.ac.uk     http://mml.materials.ox.ac.uk/NM
>
>
>
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