[Pw_forum] Phonons with DFPT and DF2 functional

[Paolo Giannozzi]

On Thu, 2014-11-06 at 13:32 -0800, Florian Altvater wrote:

> just to clarify, do Grimme-D2 or the Tkatchenko-Scheffler correction
> fall under the "vdW of any kind" category

yes

> or are they implemented in 5.1 for DFPT?

no. Any new develoment in the self-consistent code that contributes 
an energy term has to be explicitly added to the DFPT calculation. 

> 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. 

in the header of the phonon.f90 code (although in a format whose logic
I never remember). Alternatively: if you know a key variable related
to some new development, and this variable is never used in the phonon
code, it is almost certain that the new development hasn't percolated
to the phonon code.

Paolo

> 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
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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