[Pw_forum] electron-phonon calculation problem

[Paolo Giannozzi]

On Thu, Apr 14, 2016 at 3:49 PM, yelena <yelena at ipb.ac.rs> wrote:


> I keep having negative phonon frequency in gamma point, -0.00007, nowhere
> else (...) but it keeps interfering with my lambda.x calculation

and all i get is NAN for alpha2F and so on. So is there any trick to avoid
> it?


modify the lambda.f90 file and other tools so that they discard small or
negative values for frequency; or, manually set them to a small positive
number


> This is clearly numerical issue, because other modes are positive and
> phonon dispersion looks as it should be and there is no any instability.


it is a known problem (violation of the Acoustic Sum Rule in approximate
calculations) for which no solution is known, other than imposing the
Acoustc Sum Rule at the endo of the calculation

Paolo

-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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