<div dir="ltr">Dear Stefano,<div><br></div><div>Thanks for your insightful question. They should be same. </div><div><br></div><div>Value of the bandgap is almost same. (Same upto hundredth). But the shape is not exactly similar. But almost same. </div><div><br></div><div>We chose k points according to our computation resource, so that may be a reason. I used 5*5*5 k points (10 k points) for 54 atoms as brillouin zone is smaller now, so less number of k point is needed. As I use the supercell size as three times the original unit cell, so zone folding hopefully won't be a issue that much.</div><div><br></div><div>I would appreciate any correction to my understanding.</div><div><br></div><div>Thank you very much.</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Aug 1, 2016 at 7:46 PM, Stefano de Gironcoli <span dir="ltr"><<a href="mailto:degironc@sissa.it" target="_blank">degironc@sissa.it</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto"><div>Dear Mohammad,</div><div> How can be possible that the two Si calculations (54 and 2-atom cell) give different band structure ?</div><div>Aren't they both silicon ? With the same cutoff and equivalent kpoints? Shouldn't they give the same result ?<br><br>stefano <div>(sent from my phone)</div></div><div><div class="h5"><div><br>On 02 Aug 2016, at 04:45, Mohammad Abu Raihan Miah <<a href="mailto:mraihanm@eng.ucsd.edu" target="_blank">mraihanm@eng.ucsd.edu</a>> wrote:<br><br></div><blockquote type="cite"><div><div dir="ltr">Hi Stefano,<div><br></div><div>When I simulated for 54 atom Silicon and also for B doped Silicon(53+1), indirect bandgap was found. Though in the result, the conduction band minima is not in the correct position (i.e. not in 0.85 X, approximately in 0.65X). </div><div><br></div><div>For the simulation of 2 atoms, indirect bandgap is also found. The result is correct (i.e. CBM is at 0.85X)</div><div><br></div><div>As underestimation of the bandgap value is well-known problem, it is also found in both cases. But we are more interested in direct bandgap issue now.</div><div><br></div><div>Any suggestion regarding this will be a great help for me.</div><div><br></div><div>Thank you very much.</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Aug 1, 2016 at 11:40 AM, stefano de gironcoli <span dir="ltr"><<a href="mailto:degironc@sissa.it" target="_blank">degironc@sissa.it</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>Dear Mohammad,<br>
<br>
I suggest you do the following exercise:<br>
Compute the band structure of 54 atom of Si with a similar
setting to the one of your present calculation. Does it have
direct gap ? compute the DOS.<br>
Compute the band structure of Silicon in the 2-atom unit cell<br>
with celldm(1) = 10.2623467, k_points (automatic) set to 15 15
15 0 0 0 <br>
Does it have a direct gap ? compute the DOS<br>
Compare total energy, band structure and DOS in the two cases. <br>
Which calculation is correct ?<br>
<br>
stefano<div><div><br>
<br>
<br>
On 01/08/2016 20:19, Mohammad Abu Raihan Miah wrote:<br>
</div></div></div>
<blockquote type="cite"><div><div>
<div dir="ltr">Hi all,
<div><br>
</div>
<div>I am currently simulating band diagram for Phosphorus doped
Silicon. I am using 53 Si atoms and 1 P atom for computation.
When I computed the band diagram, it resulted in direct band
gap, which is not true case for Silicon. I have not relaxed
the system.</div>
<div><br>
</div>
<div>My input file is as follows,</div>
<div><br>
</div>
<div>
<div>&control</div>
<div> calculation = 'scf',</div>
<div> restart_mode='from_scratch',</div>
<div> verbosity = 'high',</div>
<div> prefix = 'Silicon_P_54_relax',</div>
<div> tstress = .true.,</div>
<div> tprnfor = .true.,</div>
<div> pseudo_dir = '.',</div>
<div> outdir = 'out_P_rel',</div>
<div> wf_collect=.true.,</div>
<div> max_seconds=10800,</div>
<div>/ </div>
<div><br>
</div>
<div>&system</div>
<div> ibrav=2,</div>
<div> celldm(1) = 30.787040,</div>
<div> nat=54, </div>
<div> ntyp=2,</div>
<div> ecutwfc=50,</div>
<div> ecutrho=400.0d0,</div>
<div> input_dft='PBE',</div>
<div> nbnd=120,</div>
<div> occupations='smearing',</div>
<div> degauss=0.05,</div>
<div>/</div>
<div><br>
</div>
<div>&electrons</div>
<div> diagonalization='david',</div>
<div> mixing_mode = 'plain',</div>
<div> mixing_beta = 0.7,</div>
<div> conv_thr = 1.0d-6,</div>
<div>/ </div>
<div><br>
</div>
<div>ATOMIC_SPECIES</div>
<div> Si 28.085500 Si.pbe-n-rrkjus_psl.0.1.UPF</div>
<div> P 30.973800 P.pbe-n-rrkjus_psl.0.1.UPF</div>
<div><br>
</div>
<div>ATOMIC_POSITIONS (alat)</div>
<div> Si 0.000000 0.000000 0.000000</div>
<div>..................................</div>
<div> P 0.083333 0.083333 0.083333<br>
</div>
<div>............................. </div>
<div>Si 0.750000 0.750000 0.750000</div>
<div><br>
</div>
<div>K_POINTS (automatic)</div>
<div> 5 5 5 0 0 0</div>
<div><br>
</div>
</div>
<div>Could anyone please explain the reason behind this change
from indirect to direct bandgap? Or any suggestion to solve
this problem?</div>
<div><br>
</div>
<div>Thank you very much.</div>
<div><br clear="all">
<div>Best,</div>
-- <br>
<div>
<div dir="ltr">
<div>
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div><span style="font-size:12.8px">Mohammad Abu
Raihan Miah</span><br>
</div>
<div>PhD Student</div>
<div><a href="http://www.ece.ucsd.edu/" target="_blank">Department of Electrical and
Computer Engineering (ECE)</a></div>
<div><a href="http://www.ucsd.edu/" target="_blank">University
of California, San Diego</a></div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<br>
<fieldset></fieldset>
<br>
</div></div><pre>_______________________________________________
Pw_forum mailing list
<a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a>
<a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a></pre>
</blockquote>
<p><br>
</p>
</div>
<br>_______________________________________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a><br>
<a href="http://pwscf.org/mailman/listinfo/pw_forum" rel="noreferrer" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><span style="font-size:12.8px">Mohammad Abu Raihan Miah</span><br></div><div>PhD Student</div><div><a href="http://www.ece.ucsd.edu/" target="_blank">Department of Electrical and Computer Engineering (ECE)</a></div><div><a href="http://www.ucsd.edu/" target="_blank">University of California, San Diego</a></div></div></div></div></div></div></div></div>
</div>
</div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br><span>Pw_forum mailing list</span><br><span><a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a></span><br><span><a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a></span></div></blockquote></div></div></div><br>_______________________________________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
<a href="http://pwscf.org/mailman/listinfo/pw_forum" rel="noreferrer" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><span style="font-size:12.8px">Mohammad Abu Raihan Miah</span><br></div><div>PhD Student</div><div><a href="http://www.ece.ucsd.edu/" target="_blank">Department of Electrical and Computer Engineering (ECE)</a></div><div><a href="http://www.ucsd.edu/" target="_blank">University of California, San Diego</a></div></div></div></div></div></div></div></div>
</div>