[Pw_forum] negtive values for TA when using q2r.x

[Katalin Gaal-Nagy]

Dear Li Yan, dear Paolo,

for me it is not clear what Le Yan exactly did (of course, I agree with 
you, Paolo!), thus, maybe some questions to Li Yan:

Which was the first grid, which you used to calculate the dispersion?

Does the 6x6x6 mesh include also the points you calculated for checking 
the negavive values?

I had a similar problem many years ago with a high-pressure phase of 
silicon, where an irregular softening appeared near Gamma, and I should 
have used a finer grid in z-direction, meaning instead of 4x4x4 something 
like 4x4x6 or 4x4x8, bcause of c/a=0.55. At least, it was not enough to go 
from a 2x2x2 to a 4x4x4 mesh.
Thus, maybe you could optimize the choice of your grid with respect to the 
lattice constants...

Best wishes,
Katalin


>>    i use q2r.x  to calculate the phonon dispersion curves for AgF.
>>    at 3GPa, there are many negative values for TA in the brillouin zone.
>>    then i just calculated one of these points, but i got a positive values.
>>    then i used  6*6*6 q mesh, no improvement is found.
>
> the Fourier interpolation performed by q2r.x yields the original phonon
> frequencies at the q-points of the grid in q-space. If it doesn't, there is
> something wrong somewhere in the procedure
>
> P.
> -- 
> Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
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