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 <[email protected]> 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://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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