[Pw_forum] Phonons with DFPT and DF2 functional

[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
> 
> ---
> Florian Altvater
> PhD candidate
> UC Berkeley/LBNL
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-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222