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

[XIAOMING ZHANG]

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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