[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
>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>
--
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20160911/ecb0f0ec/attachment.html>
More information about the users
mailing list