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<p>Sorry forgot half of the answer <br>
</p>
<p><br>
</p>
<p>acustic branches should be flat along k_z direction, I would
check that is so. If it is not so, maybe you are adding non
physical interactions between periodic images and this can cause
the numerical instabilities. I don't know whether your program
is able to clean spurious interactions due to fake periodicity. <br>
I hope this helps - pietro<br>
</p>
<div class="moz-cite-prefix">On 05/12/2016 09:52, Pietro Delugas
wrote:<br>
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<p>Then one of the 3 acustic branches ( probably the one you gave
problems with ) should be flat. <br>
</p>
<p>I don't know how this phononpy works, maybe there is a way to
deal directly with 2D systems, otherwise just find a way to set
to 0 all the interatomic force constants that correspond to
interactions between atoms staying in different periodic images
of the slab.</p>
<p><br>
</p>
<p>pietro <br>
</p>
<br>
<br>
<div class="moz-cite-prefix">On 05/12/2016 09:33, Mohammed
Ghadiyali wrote:<br>
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<blockquote
cite="mid:BN6PR06MB3042981603DD5690DB6E983ECD830@BN6PR06MB3042.namprd06.prod.outlook.com"
type="cite">
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<p>Hi,</p>
<p><br>
</p>
<p>The structure is two dimensional similar to bi-layer
graphene. </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>
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