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Dear Mohammed,
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<div class="">Have you computed your force constants for a supercell or are you inter/extrapolating q≠Gamma from the --dim=“1 1 1” force constants? If it’s 1 1 1, try to make a supercell that will give you access to the zone-boundary points so that your interpolation
becomes better.</div>
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<div class="">Best regards,</div>
<div class="">-uli</div>
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SNF Prof. Dr. Ulrich Aschauer<br class="">
Universität Bern<br class="">
Departement für Chemie und Biochemie<br class="">
Freiestrasse 3<br class="">
CH-3012 Bern<br class="">
Tel. +41 (0)31 631 5629<br class="">
<a href="mailto:ulrich.aschauer@dcb.unibe.ch" class="">ulrich.aschauer@dcb.unibe.ch</a><br class="">
<a href="http://www.dcb.unibe.ch" class="">www.dcb.unibe.ch</a><br class="">
Büro: N431</div>
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<div class="">On 5 Dec 2016, at 09:25, Pietro Delugas <<a href="mailto:pdelugas@sissa.it" class="">pdelugas@sissa.it</a>> wrote:</div>
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Hello Mohammed</div>
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If the phonon were computed with phononpy for any numerical problem maybe you will find more help in the forum of phononpy users. <span class="Apple-converted-space"> </span><br class="">
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Could you provide more information about the structure ? Is it 3D or 2D ?<span class="Apple-converted-space"> </span><br class="">
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greetings - pietro <span class="Apple-converted-space"> </span><br class="">
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On 05/12/2016 08:23, Mohammed Ghadiyali wrote:<br class="">
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<div style="margin-top: 0px; margin-bottom: 0px;" class=""><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;" class="">Dear All,</span><br class="">
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">I am working on a bilayer tin system and has performed geometry relaxation using Quantum Espresso 5.4.0 of the structure via:</div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">1. One relax calculation - for coordinate relaxation </div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">2. One vc-relax calculation with cell_do_free as 2Dxy - for coordinate and cell shape relaxation</div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class=""><span style="font-size: 12pt;" class="">3. Two vc-relax calculation with cell_do_free as shape - </span><span style="font-size: 12pt;" class="">for coordinate and cell shape relaxation with constant
volume.</span><br class="">
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">these calculations were performed with, <span style="font-size: 12pt;" class="">ecutwfc = 60 Ry and K-point mesh as 10 10 1, 1 1 1.</span></div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">Further, phonon calculations were performed using the phononpy 1.11.0 package with the same parameters. The </div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">structure <span style="font-size: 12pt;" class="">seem to gotten relaxed but it still has some negative frequencies near the Gamma point, are these's negative </span></div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">frequencies numerical instabilities or the structure is unstable.</div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">I am attaching the phonon dispersion file. Please advice.</div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">Regards,</div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">Ghadiyali Mohammed Kader.</div>
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<div style="margin-top: 0px; margin-bottom: 0px;" class="">Research Scholar,</div>
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