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On 09/30/2010 08:47 PM, Mehmet Topsakal wrote:
<blockquote
cite="mid:AANLkTi=r3=xL7_z=WvSv-dfgpn=SE7B29QOEqU2aUMoR@mail.gmail.com"
type="cite">Dear Gabriele,
<div><br>
</div>
<div>Thank you very much for your suggestion. After including some
smearing, -5000 frequencies disappeared. But this </div>
<div>still cannot explain the 3X 3X 1 situation. </div>
</blockquote>
<br>
Why is this situation so special? BTW, I cannot find any result about
this case in your repository.<br>
<br>
<blockquote
cite="mid:AANLkTi=r3=xL7_z=WvSv-dfgpn=SE7B29QOEqU2aUMoR@mail.gmail.com"
type="cite">
<div>For this reason, I plotted the positions of scf KPOINTS (see the
attachments)</div>
<div>and realized that the corner of the Brillouin zone, which is
also known as K-special-point, is NOT included for KPOINTS</div>
<div>other than 3X 3X 1. For graphene, K-special-point also
corresponds to the Dirac-Point where zero-band-gap occurs.</div>
</blockquote>
<br>
>From your nice drawing of the k-points, I guess that the "Dirac"
K-point is included also in the 9x9x1 and 12x12x1 meshes (without
shift, at least that's what your have written in the picture and in the
input files), so this may explain why you get strange results for those
meshes without smearing.<br>
<br>
<blockquote
cite="mid:AANLkTi=r3=xL7_z=WvSv-dfgpn=SE7B29QOEqU2aUMoR@mail.gmail.com"
type="cite">
<div>As a result, problem should be related with K-special-point. <br>
</div>
</blockquote>
<br>
If you include the shift I think that the K-point will never be
included (excepting the 3x3x1 grid perhaps). I suggest you to study the
convergence of the frequencies separately for the shifted and unshifted
grids (both with smearing) and see if they converge to the same result.
Some people believe that including the K-point in the BZ sampling is of
vital importance, even with dense meshes. I'm not sure of that.<br>
<br>
<blockquote
cite="mid:AANLkTi=r3=xL7_z=WvSv-dfgpn=SE7B29QOEqU2aUMoR@mail.gmail.com"
type="cite">
<div><br>
</div>
<div>BUT. Still I cannot understand why inclusion of a point in BZ
corresponds to such a HUGE difference in phonon frequencies.</div>
<div>
Maybe someone in this list gives a better explanation for that....</div>
</blockquote>
<br>
I cannot explain this, sorry. Let's wait for an answer from a graphene
or phonon expert (or both).<br>
<br>
<br>
Regards<br>
<br>
<br>
GS<br>
<br>
<blockquote
cite="mid:AANLkTi=r3=xL7_z=WvSv-dfgpn=SE7B29QOEqU2aUMoR@mail.gmail.com"
type="cite">
<div><br>
</div>
<div>All of the files are available at <span class="Apple-style-span"
style="font-family: monospace; font-size: medium; white-space: pre-wrap;"><a
moz-do-not-send="true" href="http://db.tt/xK2Jtu1">http://db.tt/xK2Jtu1</a></span></div>
<div><span class="Apple-style-span"
style="font-family: monospace; font-size: medium; white-space: pre-wrap;"><br>
</span></div>
<div><span class="Apple-style-span"
style="font-family: monospace; font-size: medium; white-space: pre-wrap;">Ragards.</span></div>
<meta http-equiv="content-type"
content="text/html; charset=ISO-8859-1">
<div><br>
</div>
<div><br>
<div class="gmail_quote">On Thu, Sep 30, 2010 at 4:47 PM, Gabriele
Sclauzero <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:sclauzer@sissa.it">sclauzer@sissa.it</a>></span> wrote:<br>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div text="#000000" bgcolor="#ffffff">
Dear Mehmet,<br>
<br>
graphene has zero gap, hence you probably need to include smearing
of the occupations in the scf calculations. <br>
<br>
<br>
HTH<br>
<br>
GS
<div>
<div class="h5"><br>
<br>
On 09/29/2010 04:54 PM, Mehmet Topsakal wrote:
</div>
</div>
<blockquote type="cite">
<div>
<div class="h5">Dear all,
<div><br>
</div>
<div>For graphene structure, I noticed that I get completely
wrong
phonon frequencies when I use KPOINTS such as 9 9 1, 12 12 1, 15 15 1</div>
<div><br>
</div>
<div>For example:<br clear="all">
<br>
</div>
<div>
<div>K_POINTS {automatic}</div>
<div>11 11 1 0 0 0 </div>
<div><br>
</div>
<div>gives realistic frequencies as in 11.phonon.out file </div>
<div><br>
</div>
<div>BUT</div>
<div><br>
</div>
<div>
<div>K_POINTS {automatic}</div>
<div>12 12 1 0 0 0 </div>
</div>
<div><br>
</div>
<div>gives "omega( 1) = -149.592762 [THz] = -4989.910586
[cm-1]"
as in 12.phonon.out</div>
<div><br>
</div>
<div><br>
</div>
<div>What should be the reason ????</div>
<div><br>
</div>
<div>Thanks.</div>
<div><br>
</div>
-- <br>
<br>
Mehmet Topsakal (Ph.D. Student)<br>
UNAM-Institute of Materials Science and Nanotechnology. <br>
Bilkent University. 06800 Bilkent, Ankara/Türkiye<br>
Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365<br>
UNAM-web : <a moz-do-not-send="true" href="http://www.nano.org.tr"
target="_blank">www.nano.org.tr</a><br>
<br>
</div>
</div>
</div>
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<br>
<br>
<pre cols="72">--
Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne
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<br clear="all">
<br>
-- <br>
<br>
<span class="Apple-style-span"
style="font-family: arial,sans-serif; font-size: 13px; border-collapse: collapse;">Mehmet
Topsakal (Ph.D. Student)</span><br>
<div>UNAM-Institute of Materials Science and Nanotechnology. <br>
Bilkent University. 06800 Bilkent, Ankara/Türkiye<br>
Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365<br>
UNAM-web : <a moz-do-not-send="true" href="http://www.nano.org.tr"
target="_blank">www.nano.org.tr</a><br>
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<br>
<pre class="moz-signature" cols="72">--
Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne
</pre>
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