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2009/10/27 DORADO Boris Thésard <boris.dorado@cea.fr>:
>
> Thank you for your answers,
>
> I used the 25x25x25 grid just to have a perfect agreement between the 
> energy differences and the force differences. And as the calculation is 
> very fast even with a 25x25x25 grid, I did not bother to reduce the grid.
>
> I intended to go back to a smaller grid but I just wanted to check the 
> reasons why the dynamical matrix would be incomplete.
>
> Thanks again for your answers. It indeed works well with the grid provided 
> in the tutorial. I guess the grid must be well chosen for the phonon 
> calculations...
>
> Regards
>
> Boris Dorado
> -----Message d'origine-----
> De : Aldo Humberto Romero [mailto:aromero@qro.cinvestav.mx]
> Envoyé : mardi 27 octobre 2009 15:43
> À : forum@abinit.org
> Objet : Re: [abinit-forum] The dynamical matrix was incomplete : phonon 
> frequencies may be wrong ...
>
> Did you check also that rfdir corresponds to the symmetry
> you are calculating?.. in cubic systems
> you just need 1 0 0 but for non-cubic .. 1 1 1 would be correct.. if you
> do not
> include them correctly, your matrices will be incomplete.
>
> Also, as Josef has pointed out, the 25x25x25 grid is quite large...you get
> excellent phonon spectra with much less, you need to use that
> fine grid for properties quite sensitive to the mesh, as the 
> electron-phonon.
> Remember that the anadbb
> utility is able to use Fourier interpolation!!!
>
> regards
>
> -aldo.
>
> -> 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
> ->
> ->
> ->
> ->
>
>
> --
>
> Prof. Aldo Humberto Romero
> CINVESTAV-Unidad Queretaro
> Libramiento Norponiente 2000
> CP 76230, Queretaro, QRO, Mexico
> tel: 442 211 9909
> fax: 442 211 9938
>
> email: aromero@qro.cinvestav.mx
>        aldorome@gmail.com
> www: qro.cinvestav.mx/~aromero
>
>