On Mon, Sep 12, 2016 at 7:43 PM, XIAOMING ZHANG <[email protected]> wrote:
do you know the reason why different computing cores lead to different > results At q=0, you should get three zero frequencies. You don't, because the calculation is approximate and violates the so-called Acoustic Sum Rule, that is, translational invariance. The main reason for such violation is the usage of a real-space grid in the calculation of the exchange-correlation potential, causing an aliasing error. The nonzero value of the "zero" frequency is unpredictable: all you know is that it is small (smaller for LDA than for GGA, almost zero if the XC potential is zero, but this is not very useful anyway). It depends upon the number of computing cores, upon the kind of parallelization, upon the compiler, the libraries, the phase of the moon, ... And How to fix it? I really confusing about this. > if you find how to fix it, you can write a nice paper. Paolo > Thanks for your time, > Xiaoming > Department of Materials Science and Engineering, > University of Utah > > > ------------------------------ > *From:* [email protected] [[email protected]] on behalf > of Paolo Giannozzi [[email protected]] > *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 > <http://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 <[email protected] > <http://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 >> >> >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> <http://redir.aspx?REF=EHU4J0HrWhueHm5YudQruShUz0Bc4ED6IfBZw8AT6HCTvLBgM9vTCAFtYWlsdG86UHdfZm9ydW1AcHdzY2Yub3Jn> >> http://pwscf.org/mailman/listinfo/pw_forum >> <http://redir.aspx?REF=3wivkGiIjv3_abLEftzZ7rrGTLe6UR2otU2wMbxCo-CTvLBgM9vTCAFodHRwOi8vcHdzY2Yub3JnL21haWxtYW4vbGlzdGluZm8vcHdfZm9ydW0.> >> > > > > -- > 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 > > > _______________________________________________ > Pw_forum mailing list > [email protected] > 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
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