[Pw_forum] negatives frequencies phonon calculation

[Ari P Seitsonen]

Dear Halima,

   (This is probably an FAQ) Did you carefully optimise the geometry and 
lattice constants before calculating the phonons? Are the imaginary 
frequencies small, maximum three of them and only at Gamma point? This 
would be "normal".

     Greetings from Zurich,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   Institut für Chemie der Universität Zürich, CH-8057 Zürich
   Tel: +41 44 63 54 497  /  Mobile: +41 79 71 90 935


On Thu, 8 May 2014, Halima Zaari wrote:

> Dear Espresso users
> I have performed a phonon calculation of an oxides on 2x2x2 q grid.   I am
> using pw.x , ph.x; q2r.x, matdyn.x and lambda.x  to calculate the 
>  phonon-electron coupling  
> . However I am getting" NAN" in the file lambda.dat and negative frequencies
> in the electron-phonon.out 
> i can't explain why i get negatives frequencies
> Kindly suggest me the possible ways where I can solve this.
> cordially
> 
> --
> H.ZAARIPhD Student in laboratory of magnetism and physics of high energy
> Faculty of Sciences in Rabat - Morocco
> Email: halimazaari at gmail.com
> 
> 
>