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<p>Hello Mohammed</p>
<p><br>
</p>
<p>If the phonon were computed with phononpy for any numerical
problem maybe you will find more help in the forum of phononpy
users. <br>
</p>
<p><br>
</p>
<p>Could you provide more information about the structure ? Is it
3D or 2D ? <br>
</p>
<p><br>
</p>
<p><br>
</p>
<p>greetings - pietro <br>
</p>
<br>
<div class="moz-cite-prefix">On 05/12/2016 08:23, Mohammed Ghadiyali
wrote:<br>
</div>
<blockquote
cite="mid:BN6PR06MB3042D0952D6AE6BC86C0BCCACD830@BN6PR06MB3042.namprd06.prod.outlook.com"
type="cite">
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"Apple Color Emoji", "Segoe UI Emoji",
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Emoji", EmojiSymbols; font-size: 16px;"> <span
style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt;">Dear All,</span><br>
</p>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif,
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<p><br>
</p>
<p>I am working on a bilayer tin system and has performed
geometry relaxation using Quantum Espresso 5.4.0 of the
structure via:</p>
<p><br>
</p>
<p><br>
</p>
<p>1. One relax calculation - for coordinate relaxation </p>
<p><br>
</p>
<p>2. One vc-relax calculation with cell_do_free as 2Dxy
- for coordinate and cell shape relaxation</p>
<p><br>
</p>
<p><span style="font-size: 12pt;">3. Two vc-relax
calculation with cell_do_free as shape - </span><span
style="font-size: 12pt;">for coordinate and cell shape
relaxation with constant volume.</span><br>
</p>
<p><br>
</p>
<p><br>
</p>
<p>these calculations were performed with, <span
style="font-size: 12pt;">ecutwfc = 60 Ry and K-point
mesh as 10 10 1, 1 1 1.</span></p>
<p><br>
</p>
<p>Further, phonon calculations were performed using the
phononpy 1.11.0 package with the same parameters. The </p>
<p><br>
</p>
<p>structure <span style="font-size: 12pt;">seem to gotten
relaxed but it still has some negative frequencies near
the Gamma point, are these's negative </span></p>
<p><br>
</p>
<p>frequencies numerical instabilities or the structure is
unstable.</p>
<p><br>
</p>
<p><br>
</p>
<p>I am attaching the phonon dispersion file. Please advice.</p>
<p><br>
</p>
<p><br>
</p>
<p>Regards,</p>
<p><br>
</p>
<p>Ghadiyali Mohammed Kader.</p>
<p><br>
</p>
<p>Research Scholar,</p>
<p><br>
</p>
<p>University of Mumbai.</p>
</div>
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