[Pw_forum] error on phonon calculation (root not converged)

[Nicola Marzari]

> I have a feeling (could be wrong) that this might be due to LDA-PP of
> Strontium.
> Since i did the same calculation for PbTiO3 using the same PPs of Ti and
> O as
> those in SrTiO3 and it worked well. So I appreciate if someone could
> send me
> your Sr LDA-PP (if you have one) that i could try.


Hi Liping,

it's indeed baffling. Do check that your coordinates are scaled
correctly - i.e. that the atoms in cartesian coordinates are
were they should be, that the axes are what they should be.

Next, if you use the same identical input files, but you put
Pb instead of Sr, do you get identical dielectric constants
from 1x1x1 and 2x2x1 ?

If you do, I admit that one would be tempted to blame the
pseudopotential, but it is still unlikely. Have a look at the
eigenvalues in the two calculations - do they match exactly ?

Let us know what you find,

			nicola

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