[Pw_forum] Phonons with DFPT and DF2 functional

[Florian Altvater]

Hello again,
just to clarify, do Grimme-D2 or the Tkatchenko-Scheffler correction
fall under the "vdW of any kind" category, or are they implemented in
5.1 for DFPT?

Also, I don't feel comfortable enough with the code yet to be able to
find that information in the source, but I am sure it is in there
somewhere. If you want to give me any pointers, so that I could
potentially answer those questions myself in the future, I would greatly
appreciate it.

Thanks,
Florian


Am 05.11.2014 um 11:06 schrieb Paolo Giannozzi:
> On Wed, 2014-11-05 at 03:51 -0800, Florian Altvater wrote:
>> Hi,
>> I am interested in looking at effects of using van der Waals functionals
>> like vdW-DF2 on the phonon dispersion of organic crystals. Preliminary
>> results indicate that there might be some issues with using DFPT and DF2
>> together. More specifically, DFPT gives a couple "very imaginary"
>> frequencies (below -100cm^-1) for Gamma-point phonons (with and without
>> acoustic sum rule), while finite displacement results seem to be just
>> fine, using the same convergence parameters.
>>
>> So before I dig deeper into eventual other issues at play here, I wanted
>> to ask if you know of any incompatibilities when using DFPT and vdW-DF2?
> DFPT + vdW (any kind) is not currently implemented. The next version
> (out in a few days) will contain a check on this
>
> Paolo
>
>> Either inherently embedded in the underlying theory (which I could then
>> dig into first), or just in the way it is implemented in QE.
>>
>> Thanks for your help,
>> Florian
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---
Florian Altvater
PhD candidate
Neaton group
UC Berkeley/LBNL