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Re: [abinit-forum] The dynamical matrix was incomplete : phonon frequencies may be wrong ...

From: Josef Zwanziger <jzwanzig@gmail.com>
To: forum@abinit.org
Subject: Re: [abinit-forum] The dynamical matrix was incomplete : phonon frequencies may be wrong ...
Date: Tue, 27 Oct 2009 11:42:20 -0300
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Hi,
all works best if the q-points you use are differences of the k-points
you use (q = k1 - k2). This is discussed in the tutorial, you can make
an auxiliary run with your new kpt grid, with no shifts, and use the
output kpts as the input q points in your phonon calculation. At
25x25x25 you will have A LOT of qpoints to calculate!!

Josef W. Zwanziger
Professor of Chemistry
Canada Research Chair in NMR Studies of Materials
Director, Nuclear Magnetic Resonance Research Resource (NMR-3)
Dalhousie University
Halifax, NS B3H 4J3 Canada
tel: +1 (902) 494-1960
fax: +1 (902) 494-1867
web: http://jwz.chem.dal.ca
jzwanzig@gmail.com, jzwanzig@dal.ca

On Tue, Oct 27, 2009 at 11:37 AM, DORADO Boris Thésard
<boris.dorado@cea.fr> wrote:
> Dear Abinit users,
>
>
>
> I’m currently trying to perform some calculations of phonon frequencies in
> AlAs, as is done in the first tutorial of the Abinit website.
>
>
>
> I changed, however, some parameters in order to have a better accuracy of
> phonon frequencies and to assess the variation of the frequencies with
> respect to the cutoff and the kpt sampling. I therefore set the cutoff to
> 400 eV (about 15 Ha, 3 Ha in the tutorial) and the kpt grid to 25x25x25, but
> the calculation of the phonon perturbation displays this warning along with
> the phonon frequencies:
>
>
>
> chkph3 : WARNING -
>
> The dynamical matrix was incomplete : phonon frequencies may be wrong ...
>
>
>
> Could someone please tell me why the dynamical matrix would be incomplete?
> Does it have anything to do with my changed calculation parameters? Because
> I kept the same input file as in the tutorial except I changed the cutoff
> and the kpt sampling. I also checked the output file of the tutorial and
> this warning of course does not appear.
>
>
>
> In addition, my phonon frequencies are indeed wrong (308 cm-1 and 337 cm-1,
> instead of something like 359 cm-1 and 390 cm-1).
>
>
>
> Thank you for your answers.
>
>
>
> Regards
>
>
>
> Boris Dorado
>
>

[abinit-forum] The dynamical matrix was incomplete : phonon frequencies may be wrong ..., DORADO Boris Thésard, 10/27/2009
- Re: [abinit-forum] The dynamical matrix was incomplete : phonon frequencies may be wrong ..., Josef Zwanziger, 10/27/2009
- Re: [abinit-forum] The dynamical matrix was incomplete : phonon frequencies may be wrong ..., Aldo Humberto Romero, 10/27/2009
  - RE: [abinit-forum] The dynamical matrix was incomplete : phonon frequencies may be wrong ..., DORADO Boris Thésard, 10/27/2009
    - Re: [abinit-forum] The dynamical matrix was incomplete : phonon frequencies may be wrong ..., bin chen, 10/28/2009