The ABINIT Users Mailing List ( CLOSED )

[Matthieu Verstraete <mjv500@york.ac.uk>]

Hello all,

You normally need the Berry phase only for finite electric 
fields/polarizations (or indeed magnetic fields, which is not in abinit at 
all).

What you want is the phonon (finite w) contribution to the non-linear 
susceptibilities. This should be available from dfpt, as post-processing, 
just as the dielectric tensor is. However I don't know off the top of my 
head which derivatives will appear. You will need a perturbation wrt an 
electric field, but this is already possible in abinit with the d/dk 
operator. The total static NL susceptibility is not implemented in abinit 
as far as I know. You may need some extra derivatives from abinit (3rd 
order) and you'll need to play with anaddb a bit to put the pieces 
together.

Pwscf may have some things like this. The groups in Regensburg and Trieste 
did some higher order dfpt, though I don't remember any finite freq NL 
dielectric constants.

Matthieu


On Mon, 7 Aug 2006, Stephane BECU wrote:

> Abinit computes the electronic dielectric tensor via a linear response
> calculation (2nd derivative of the energy) from DFPT. It also computes the
> static dielectric tensor (at finite frequencies ie the ionic part of the
> dielectric tensor) and the ELECTONIC NON-LINEAR susceptibilities via a
> non-linear response calculation (3rd derivative of the energy) from DFPT.
> What I am interested in are the STATIC NON-LINEAR susceptibilities (at
> finite frequencies). In fact I think it is not available from DFPT with
> abinit, but I think it could be possible to calculate them from a Berry
> phase calculation. Am I right?
>
> Stéphane
>
> -----Original Message-----
> From: Anglade Pierre-Matthieu [mailto:anglade@gmail.com]
> Sent: Monday, August 07, 2006 9:11 AM
> To: forum@abinit.org
> Subject: Re: [abinit-forum] NON-LINEAR SUSCEPTIBILITIES
>
>
> I really don't know (answere for each of your questions). Yet since no one
> has answered your first question after three days I guess that it means that
> this is not done within abinit. In fact I'm just wondering about what you
> mean by "nonlinear" susceptibilities ? What's the difference between this
> and the susceptibility matrix computed within abinit ? Would you mind
> teaching me (if this can be done in a few
> words) about this ?
>
> PMA
>
> On 8/7/06, Stephane BECU <stephane.becu@st.com> wrote:
> > Hi Pierre-Matthieu,
> >
> > Do you mean that such equations have to be implemented in the ABINIT
> > code? Do you know if the other existing ab-initio  packages (e.g. the
> > Vienna ab-initio simulation package VASP or any other one) have ever
> > done such calculations?
> >
> > Thanks again for your help
> >
> > Stéphane
> > -----Original Message-----
> > From: Anglade Pierre-Matthieu [mailto:anglade@gmail.com]
> > Sent: Monday, August 07, 2006 8:34 AM
> > To: forum@abinit.org
> > Subject: Re: [abinit-forum] NON-LINEAR SUSCEPTIBILITIES
> >
> >
> > Hi,
> >
> > If you have a formula for this kind of thing, since abinit is GPL, you
> > can do it :-)
> >
> > regards
> >
> > PMA
> >
> > On 8/4/06, Stephane BECU <stephane.becu@st.com> wrote:
> > > Dear all,
> > >
> > > Do you if it is possible to compute non-linear susceptibilities at
> > > finite frequencies with abinit?
> > >
> > > Thanks for your help,
> > >
> > > Stéphane Bécu

--
================================================================
Dr. Matthieu Verstraete                 mailto:mjv500@york.ac.uk
Dept. of Physics, University of York,     tel: +44 1904 43 22 08
Heslington, YO10 5DD York, United Kingdom fax: +44 1904 43 22 14