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<font face="monospace" size="3">Dear Paolo:<br>
<br>
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.<br>
<br>
Thanks for your time,<br>
Xiaoming<br>
Department of Materials Science and Engineering, </font>
<div><font face="monospace" size="3">University of Utah</font>
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<div id="divRpF266754" style="direction: ltr;"><font face="Tahoma" size="2" color="#000000"><b>From:</b> pw_forum-bounces@pwscf.org [pw_forum-bounces@pwscf.org] on behalf of Paolo Giannozzi [p.giannozzi@gmail.com]<br>
<b>Sent:</b> Sunday, September 11, 2016 12:51 PM<br>
<b>To:</b> PWSCF Forum<br>
<b>Subject:</b> Re: [Pw_forum] different computing cores lead to different results when calculating phonon spectrum by ph.x<br>
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<div>The frequencies you report are 0 by definition, almost 0 when computed: <a href="redir.aspx?REF=4sg-3oovjh9dbihtpRKtW8iIgpzbkIFFdTzPFukAKJtulrBgM9vTCAFodHRwOi8vd3d3LnF1YW50dW0tZXNwcmVzc28ub3JnL2ZhcS9waG9ub25zLyM3LjI." target="_blank">
http://www.quantum-espresso.org/faq/phonons/#7.2</a> . No available solution other than imposing the Acoustic Sum Rule (ASR) afterwards.<br>
Basically, the ASR violation is numerical noise, and as such, rather unpredictable.<br>
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<div>Paolo<br>
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<div class="gmail_quote">On Sun, Sep 11, 2016 at 8:10 PM, XIAOMING ZHANG <span dir="ltr">
<<a href="redir.aspx?REF=rcdX65FVruQA1h4tbMGDKMD1AbCtgbuH3RWw8G8Mz0pulrBgM9vTCAFtYWlsdG86eGlhb20uemhhbmdAdXRhaC5lZHU." target="_blank">xiaom.zhang@utah.edu</a>></span> wrote:<br>
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<pre>Dear all,</pre>
<pre>I have several questions when calculating phonons by ph.x:</pre>
<pre>(1) Using the same input files, I got different output files of dynamical matrices when using different computing cores; </pre>
<pre>take q = ( 0.000000000 0.000000000 0.000000000 ) as an example:</pre>
<pre>Using 96 computing cores, the results a<span style="font-size:10pt">fter the line "Dynamical Matrix in cartesian axes"</span></pre>
<pre>and the q-value are:</pre>
<pre> ******************************<wbr>******************************<wbr>**************
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 )</pre>
<pre>However, when I using 128 computing cores, the corresponding results turn to be:</pre>
<pre>******************************<wbr>******************************<wbr>**************
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 )</pre>
<pre>So, why do different computing cores lead to different results? Does someone encounter the same problems?</pre>
<pre>By the way, is it reasonable for the negative frequency (such as <span style="font-size:13.3333px">freq ( 1) = -1.940214 [THz] = -64.718584 [cm-1]</span><span style="font-size:10pt">) ?</span></pre>
<pre><span style="font-size:10pt"><br></span></pre>
<pre><span style="font-size:10pt">(2) With different computing cores, I always get the p</span>honon spectrum with small imaginary frequency no matter how I <span style="font-size:10pt">adjust the parameters suggested by other guys</span><span style="font-size:10pt">. </span></pre>
<pre><span style="font-size:10pt">S</span><span style="font-size:10pt">o can someone give me some useful suggestions to </span>eliminate<span style="font-size:10pt"> the </span><span style="font-size:13.3333px">imaginary frequency</span><span style="font-size:10pt">?</span></pre>
<pre><br></pre>
<pre>Thanks for <font size="3">your time,</font></pre>
<pre><font size="3">Xiaoming</font></pre>
<pre><span style="white-space:normal"><font size="3">Department of Materials Science and Engineering, University of Utah</font></span></pre>
<pre><span style="font-size:10pt"><br></span></pre>
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<div>Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,<br>
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy<br>
Phone +39-0432-558216, fax +39-0432-558222<br>
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