[Pw_forum] ph - computational errors in vicinity of gamma point

[Gabriele Sclauzero]

OK, I see, it is the acoustic phonon that gets imaginary. Then you are 
right, it is an accuracy issue, but it can be fixed by imposing the 
Acoustic Sum Rule in the dynmat.x or matdyn.x run (see PHonon/example02, 
for instance). Otherwise you would have to raise cutoffs and number of 
k-points to very high values in order to get a decent frequency.

Gabriele




On 08/20/2014 11:13 AM, Kvasov Alexander wrote:
> Dear Gabriele,
> yes, I changed the volume, it's less then the relaxed value. this way 
> TO phonon is stable at gamma point.
> the right values for TA branch should go to 0.
> Alexander


-- 
Dr. Gabriele Sclauzero
ETH Zurich
Materials Theory
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Phone +41 44 633 94 10
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gabriele.sclauzero at mat.ethz.ch
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