[Pw_forum] different computing cores lead to different results when calculating phonon spectrum by ph.x
XIAOMING ZHANG
xiaom.zhang at utah.edu
Mon Sep 12 19:43:43 CEST 2016
Dear Paolo:
Thanks for your quick reply. But do you know the reason why different computing cores lead to different results? And How to fix it? I really confusing about this.
Thanks for your time,
Xiaoming
Department of Materials Science and Engineering,
University of Utah
________________________________
From: pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] on behalf of Paolo Giannozzi [p.giannozzi at gmail.com]
Sent: Sunday, September 11, 2016 12:51 PM
To: PWSCF Forum
Subject: Re: [Pw_forum] different computing cores lead to different results when calculating phonon spectrum by ph.x
The frequencies you report are 0 by definition, almost 0 when computed: http://www.quantum-espresso.org/faq/phonons/#7.2<redir.aspx?REF=4sg-3oovjh9dbihtpRKtW8iIgpzbkIFFdTzPFukAKJtulrBgM9vTCAFodHRwOi8vd3d3LnF1YW50dW0tZXNwcmVzc28ub3JnL2ZhcS9waG9ub25zLyM3LjI.> . 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<redir.aspx?REF=rcdX65FVruQA1h4tbMGDKMD1AbCtgbuH3RWw8G8Mz0pulrBgM9vTCAFtYWlsdG86eGlhb20uemhhbmdAdXRhaC5lZHU.>> 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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