[Wien] Suggestions on PHONON Calculation 4

[Peter Blaha]

If your supercell contains only 12 atoms ?? it is a very small supercell.

Thus only on very few q-points the phonons will be correct, while using such a small
cell the phonons on other q-points can be completely wrong.

When you plot the force constants, you should see that the far distance f.c. are still not
converged (small).

No, I don't want you dsy file.

When the "sum of forces" during analyse_phonon are small for every displacement, there
is no problem with the WIEN2k calculations.

Please read the phonon manual. It is clearly said there, that you need a sizable supercell!

Am 10.02.2011 13:13, schrieb Ghosh SUDDHASATTWA:
> Dear Dr.Blaha,
>
> I am sorry I have posted this question before.
>
> I guess my querie may be inappropriate in the Wien2k mailing list. Still, first I would request Prof. Blaha to kindly give me permission and help me in sorting the issue in PHONON
> which actually is not a Wien2k problem.
>
> After I imported the case.dsy file ( forces convergence obtained with 0.005 mRy) in phonon software and incorporated the lattice parameters of the supercell and the number of
> atoms, I applied the translational and rotational invariances, I get the Do Report in PHONON.
>
> I get the plot of force constants and I subsequently get the phonon dispersion. I get some imaginary frequencies which I am not sure if it is because of the wrong choice of
> supercell size (12 atoms) or the force convergence (0.005 mRy/atom)
>
> Can you please help me in this regard?
>
> Can I send you the case.dsy for your perusal?
>
> Thank you
>
> Suddhasattwa
>
>
>
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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