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<p>Dear Chin S. <br>
</p>
<p>Your system is metallic from the point of view of DFT which is
not a surprise. <br>
</p>
<p>In your last calculation, which is the more accurate you simply
catch this fact ... In other words in your previous calculations
you had 0.1 eV gap due to less kpoints and/or less accurate
calculations. To really understand what is happening you should
draw the DOS and bandstructure to see if you have band crossing at
the Fermi level which could lead to occupancy of an expected empty
band. If yes, it will have an impact on the chemical bond
description and also on the phonons. <br>
</p>
<p>Depending on the system you will have to consider methods going
beyond DFT, which in WIEN2k could be based on: <br>
</p>
<p>- DFT+U</p>
<p>- Onsite Hybrid functional</p>
<p>- Full hybrid <br>
</p>
<p>- TB-mBJ potential</p>
<p>If your band gap is based on charge transfer transitions you
cannot used DFT+U and onsite-hybrid. <br>
Thus the less expensive approach will be TB-mBJ potential which
will give the band gap but not the forces. <br>
</p>
<p>Thus only one option remains which is full hybrid. <br>
</p>
<p>If your system is based on d-d transitions, or highly correlated
states, then you can used DFT+U or Onsite-hybrid. <br>
</p>
<p>Hope it will help you. <br>
</p>
<p>Cheers</p>
<p>Xavier<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">Le 27/01/2018 à 12:28, chin Sabsu a
écrit :<br>
</div>
<blockquote
cite="mid:748258925.1577703.1517052488594@mail.yahoo.com"
type="cite">
<div style="font-family:Helvetica Neue, Helvetica, Arial,
sans-serif;font-size:16px;">
<div style="font-family: Helvetica, Arial, sans-serif;
font-size: 16px;">
<div>Dear Stefaan Sir</div>
<div><br>
</div>
<div>Below are my updates:</div>
<div><br>
</div>
<div>A. For mesh size</div>
<div>I got your point and in all different distorted structure
(with different inequivalent atoms) I am having the same
number of electrons while the number of inequivalent atoms <g
class="gr_ gr_167 gr-alert gr_gramm gr_inline_cards
gr_run_anim Grammar multiReplace" id="167"
data-gr-id="167">are</g> different. NE varies from 154 to
616(1x1x1 cell) to 4928 (2x2x2 cell).</div>
<div>So I will divide xxx <g class="gr_ gr_203 gr-alert
gr_spell gr_inline_cards gr_run_anim ContextualSpelling
ins-del multiReplace" id="203" data-gr-id="203">numk</g>
by 4 and 32 in 1x1x1 and 2x2x2 supercell structure. Thanks
for this excellent recommendation!!!</div>
<div>For 2x2x2 supercell in <g class="gr_ gr_1811 gr-alert
gr_spell gr_inline_cards gr_run_anim ContextualSpelling"
id="1811" data-gr-id="1811">phonopy</g> calculations, we
need to go for <g class="gr_ gr_1775 gr-alert gr_spell
gr_inline_cards gr_disable_anim_appear ContextualSpelling
ins-del multiReplace" id="1775" data-gr-id="1775">mpi</g>
jobs for certain cases!!<br>
</div>
<div><br>
</div>
<div>B. Now I have done some tests for my cubic perovskite and
below are my observations:</div>
<div><br>
</div>
<div>B1. For <g class="gr_ gr_1681 gr-alert gr_spell
gr_inline_cards gr_disable_anim_appear ContextualSpelling"
id="1681" data-gr-id="1681">tolf</g> 5 and -fc1 I for
FOR003 = ~4 <g class="gr_ gr_528 gr-alert gr_spell
gr_inline_cards gr_disable_anim_appear ContextualSpelling
ins-del multiReplace" id="528" data-gr-id="528">mRy</g>/<g
class="gr_ gr_527 gr-alert gr_spell gr_inline_cards
gr_disable_anim_appear ContextualSpelling ins-del
multiReplace" id="527" data-gr-id="527">bohr</g> with
band gap ~0.1 eV<br>
</div>
<div>B2. For <g class="gr_ gr_551 gr-alert gr_spell
gr_inline_cards gr_disable_anim_appear ContextualSpelling"
id="551" data-gr-id="551">tolf</g> 2 and -<g class="gr_
gr_568 gr-alert gr_spell gr_inline_cards
gr_disable_anim_appear ContextualSpelling ins-del
multiReplace" id="568" data-gr-id="568">fc</g> 0.1 forces
are almost same. and the band gap is still ~0.1ev<br>
</div>
<div><br>
</div>
<div>B3. Now to reduce the forces less then 0.1mRy/<g
class="gr_ gr_1018 gr-alert gr_spell gr_inline_cards
gr_disable_anim_appear ContextualSpelling ins-del
multiReplace" id="1018" data-gr-id="1018">bohr</g>, I
reduced the <g class="gr_ gr_1073 gr-alert gr_spell
gr_inline_cards gr_disable_anim_appear ContextualSpelling
ins-del multiReplace" id="1073" data-gr-id="1073">tolf</g>
to 0.5 and -<g class="gr_ gr_1105 gr-alert gr_spell
gr_inline_cards gr_disable_anim_appear ContextualSpelling
ins-del multiReplace" id="1105" data-gr-id="1105">fc</g>
0.1 - 0.01. I got forces at the desired <g class="gr_
gr_1656 gr-alert gr_spell gr_inline_cards
gr_disable_anim_appear ContextualSpelling ins-del
multiReplace" id="1656" data-gr-id="1656">accurecy</g> but
the band gap vanished and the system becomes metallic. The
experimentally reported band gap is 1.2eV<br>
</div>
<div>I used <g class="gr_ gr_1443 gr-alert gr_spell
gr_inline_cards gr_disable_anim_appear ContextualSpelling
ins-del multiReplace" id="1443" data-gr-id="1443">RKMAX</g>
8, <g class="gr_ gr_1468 gr-alert gr_spell gr_inline_cards
gr_disable_anim_appear ContextualSpelling ins-del
multiReplace" id="1468" data-gr-id="1468">numk</g> 2000, <g
class="gr_ gr_1523 gr-alert gr_spell gr_inline_cards
gr_disable_anim_appear ContextualSpelling" id="1523"
data-gr-id="1523">vxc</g> 19.</div>
<div><br>
</div>
<div>What is your suggestion for point number B, why I am
getting the system metallic?</div>
<div>Can I use this relaxed structure for Phonopy?</div>
<div><br>
</div>
<div>Kind regards</div>
<div><br>
</div>
<div>Chin S.</div>
<div><br>
</div>
<div> <br>
</div>
<div>For t<g class="gr_ gr_656 gr-alert gr_spell
gr_inline_cards gr_disable_anim_appear ContextualSpelling
ins-del multiReplace" id="656" data-gr-id="656">olf</g><br>
</div>
<div><br>
</div>
</div>
</div>
<br>
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<br>
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