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<p style="margin-top:0;margin-bottom:0">Hello <span>Yusuf</span>,</p>
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<p style="margin-top:0;margin-bottom:0">A negative phonon frequency can be a sign that your material is dynamically unstable to vibrations.</p>
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<p style="margin-top:0;margin-bottom:0">This does not pose a problem in calculating Tc values. You can include the negative frequencies and Tc will be slightly reduced, or you can manually cut them out if you think it makes more
<span>sense</span> in your case. <br>
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<p style="margin-top:0;margin-bottom:0">Hope this helps, if you have any more questions, feel free to ask,</p>
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<p style="margin-top:0;margin-bottom:0">Craig Tenney</p>
<p style="margin-top:0;margin-bottom:0">Washington State University</p>
<p style="margin-top:0;margin-bottom:0">Graduate Student<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of Yusuf Zuntu <yzunt@yahoo.com><br>
<b>Sent:</b> Thursday, March 22, 2018 9:41:23 PM<br>
<b>To:</b> users@lists.quantum-espresso.org<br>
<b>Subject:</b> [QE-users] Question on negative phonon frequency at Gamma point</font>
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<div>Dear all,<br>
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<div>Please how do you get rid of a negative phonon frequency at a Gamma point. I have done some trial calculations for two different 2D materials. Please find the results details below:</div>
<div><br>
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<div>System 1:</div>
<div><br>
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<div>ph.x results at Gamma point</div>
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<div> q = ( 0.000000000 0.000000000 0.000000000 ) <br>
<br>
**************************************************************************<br>
freq ( 1) = -0.716980 [THz] = -23.915891 [cm-1]<br>
freq ( 2) = 1.170257 [THz] = 39.035571 [cm-1]<br>
freq ( 3) = 2.301718 [THz] = 76.777040 [cm-1]<br>
freq ( 4) = 4.692676 [THz] = 156.530836 [cm-1]<br>
freq ( 5) = 6.547729 [THz] = 218.408714 [cm-1]<br>
freq ( 6) = 7.575469 [THz] = 252.690440 [cm-1]<br>
freq ( 7) = 7.954771 [THz] = 265.342590 [cm-1]</div>
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<div>matdyn.x results</div>
<div><br>
</div>
<div>diagonalizing the dynamical matrix ...<br>
<br>
q = 0.0000 0.0000 0.0000<br>
**************************************************************************<br>
freq ( 1) = -0.168246 [THz] = -5.612090 [cm-1]<br>
( -0.205675 0.000000 -0.162406 0.000000 -0.049537 0.000000 )<br>
( -0.204095 0.000000 -0.166786 0.000000 -0.047497 0.000000 )<br>
( -0.202604 0.000000 -0.168584 0.000000 -0.038435 0.000000 )<br>
( -0.204187 0.000000 -0.166901 0.000000 -0.037977 0.000000 )<br>
( -0.204822 0.000000 -0.164879 0.000000 -0.035645 0.000000 )<br>
( -0.204067 0.000000 -0.159939 0.000000 -0.043878 0.000000 )<br>
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<div>System 2:</div>
<div><br>
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<div>ph.x results at Gamma point</div>
<div><br>
</div>
<div> q = ( 0.000000000 0.000000000 0.000000000 ) <br>
<br>
**************************************************************************<br>
omega( 1) = -2.676536 [THz] = -89.279630 [cm-1]<br>
omega( 2) = 2.176387 [THz] = 72.596456 [cm-1]<br>
omega( 3) = 2.268904 [THz] = 75.682505 [cm-1]<br>
omega( 4) = 2.781243 [THz] = 92.772280 [cm-1]<br>
omega( 5) = 2.831070 [THz] = 94.434329 [cm-1]<br>
omega( 6) = 5.362633 [THz] = 178.878184 [cm-1]<br>
omega( 7) = 5.391573 [THz] = 179.843530 [cm-1]</div>
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</div>
<div><br>
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<div>matdyn.x results </div>
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<div>diagonalizing the dynamical matrix ...<br>
<br>
q = 0.0000 0.0000 0.0000<br>
**************************************************************************<br>
omega( 1) = -0.081634 [THz] = -2.723002 [cm-1]<br>
( -0.270214 0.000000 -0.101393 0.000000 -0.001203 0.000000 )<br>
( -0.270014 0.000000 -0.100654 0.000000 0.001122 0.000000 )<br>
( -0.270492 0.000000 -0.099822 0.000000 0.003548 0.000000 )<br>
( -0.270726 0.000000 -0.100219 0.000000 0.003104 0.000000 )<br>
( -0.271070 0.000000 -0.100621 0.000000 0.006056 0.000000 )<br>
( -0.270797 0.000000 -0.101038 0.000000 0.002118 0.000000 )<br>
( -0.270725 0.000000 -0.100220 0.000000 -0.002122 0.000000 )<br>
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<div>Lastly, do you think the results above will affect Tc calculations. If Yes, please advice me on what to do to remove the negative frequencies in both cases.</div>
<div><br>
</div>
Yusuf Zuntu</div>
<div>PhD candidate</div>
<div>School of Physics</div>
<div>USM, Maalysia<br>
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