[Pw_forum] negatives frequencies phonon calculation

[Halima Zaari]

I already optimized the geometry and lattice constants. i get the following
value

 Diagonalizing the dynamical matrix

     q = (    0.000000000   0.000000000   0.000000000 )

 **************************************************************************
     omega( 1) =     -18.907308 [THz] =    -630.679895 [cm-1]
     omega( 2) =     -18.907308 [THz] =    -630.679895 [cm-1]
     omega( 3) =     -18.907308 [THz] =    -630.679895 [cm-1]
     omega( 4) =     -13.087809 [THz] =    -436.562323 [cm-1]
     omega( 5) =     -13.087809 [THz] =    -436.562323 [cm-1]
     omega( 6) =       2.252439 [THz] =      75.133272 [cm-1]


2014-05-08 11:29 GMT+01:00 Ari P Seitsonen <Ari.P.Seitsonen at iki.fi>:

>
> 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
>>
>>
>>
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-- 
H.ZAARI
PhD Student in laboratory of magnetism and physics of high energy
Faculty of Sciences in Rabat - Morocco
Email:
* halimazaari at gmail.com <boujnah.mourad at gmail.com>*
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