[Pw_forum] different computing cores lead to different results when calculating phonon spectrum by ph.x

Paolo Giannozzi p.giannozzi at gmail.com
Sun Sep 11 20:51:24 CEST 2016


The frequencies you report are 0 by definition, almost 0 when computed:
http://www.quantum-espresso.org/faq/phonons/#7.2 . No available solution
other than imposing the Acoustic Sum Rule (ASR) afterwards.
Basically, the ASR violation is numerical noise, and as such, rather
unpredictable.

Paolo

On Sun, Sep 11, 2016 at 8:10 PM, XIAOMING ZHANG <xiaom.zhang at utah.edu>
wrote:

> Dear all,
>
> I have several questions when calculating phonons by ph.x:
>
> (1) Using the same input files, I got different output files of dynamical matrices when using different computing cores;
>
> take q = (    0.000000000   0.000000000   0.000000000 ) as an example:
>
> Using 96 computing cores, the results after the line "Dynamical Matrix in cartesian axes"
>
> and the q-value are:
>
>  **************************************************************************
>      freq (    1) =      -1.940214 [THz] =     -64.718584 [cm-1]
>  (  0.000000  0.000000 -0.000000  0.000000 -0.237593  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.237593  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.237593  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.237593  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.237593  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.237593  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.209687  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.209687  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.209687  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.209687  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.209687  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.209687  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.363998  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.363998  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.363998  0.000000 )
>      freq (    2) =       0.946381 [THz] =      31.567870 [cm-1]
>  (  0.000000  0.000000 -0.000000  0.000000 -0.101981  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.101981  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000  0.101979  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000  0.101979  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000  0.000001  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000  0.000001  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.384498  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000 -0.384498  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000  0.384493  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000  0.384493  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000  0.000005  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000  0.000005  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000  0.428402  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000 -0.428397  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.000006  0.000000 )
>      freq (    3) =       0.946381 [THz] =      31.567870 [cm-1]
>  (  0.000000  0.000000 -0.000000  0.000000 -0.058877  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.058877  0.000000 )
>  (  0.000000  0.000000 -0.000000  0.000000 -0.058879  0.000000 )
>
> However, when I using 128 computing cores, the corresponding results turn to be:
>
> **************************************************************************
>      freq (    1) =      -1.941478 [THz] =     -64.760743 [cm-1]
>  ( -0.000000  0.000000 -0.000000  0.000000  0.237504  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.237504  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.237504  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.237504  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.237504  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.237504  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.209612  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.209612  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.209612  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.209612  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.209612  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.209612  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.364201  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.364201  0.000000 )
>  ( -0.000000  0.000000 -0.000000  0.000000  0.364201  0.000000 )
>      freq (    2) =      -0.797967 [THz] =     -26.617308 [cm-1]
>  ( -0.217955  0.000000 -0.132999  0.000000 -0.000000  0.000000 )
>  ( -0.217955  0.000000 -0.132999  0.000000 -0.000000  0.000000 )
>  ( -0.212134  0.000000 -0.133209  0.000000  0.000000  0.000000 )
>  ( -0.212134  0.000000 -0.133209  0.000000  0.000000  0.000000 )
>  ( -0.215227  0.000000 -0.138145  0.000000  0.000000  0.000000 )
>  ( -0.215227  0.000000 -0.138145  0.000000  0.000000  0.000000 )
>  ( -0.230258  0.000000 -0.129133  0.000000 -0.000000  0.000000 )
>  ( -0.230258  0.000000 -0.129133  0.000000 -0.000000  0.000000 )
>  ( -0.205571  0.000000 -0.130026  0.000000  0.000000  0.000000 )
>  ( -0.205571  0.000000 -0.130026  0.000000  0.000000  0.000000 )
>  ( -0.218687  0.000000 -0.150959  0.000000  0.000000  0.000000 )
>  ( -0.218687  0.000000 -0.150959  0.000000  0.000000  0.000000 )
>  ( -0.228822  0.000000 -0.140474  0.000000  0.000000  0.000000 )
>  ( -0.224086  0.000000 -0.140645  0.000000 -0.000000  0.000000 )
>  ( -0.226602  0.000000 -0.144661  0.000000 -0.000000  0.000000 )
>      freq (    3) =      -0.797967 [THz] =     -26.617308 [cm-1]
>  ( -0.136570  0.000000  0.212256  0.000000 -0.000000  0.000000 )
>  ( -0.136570  0.000000  0.212256  0.000000 -0.000000  0.000000 )
>  ( -0.136360  0.000000  0.218077  0.000000  0.000000  0.000000 )
>
> So, why do different computing cores lead to different results? Does someone encounter the same problems?
>
> By the way, is it reasonable for the negative frequency (such as freq (    1) =      -1.940214 [THz] =     -64.718584 [cm-1]) ?
>
>
> (2) With different computing cores, I always get the phonon spectrum with small imaginary frequency no matter how I adjust the parameters suggested by other guys.
>
> So can someone give me some useful suggestions to eliminate the imaginary frequency?
>
>
> Thanks for your time,
>
> Xiaoming
>
> Department of Materials Science and Engineering, University of Utah
>
>
>
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>



-- 
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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