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<p>Could you give the chemical formula? It will really help
answering your question from my side. <br>
</p>
<p>Cheers</p>
<p>Xavier<br>
</p>
<br>
<div class="moz-cite-prefix">Le 27/01/2018 à 14:34, chin Sabsu a
écrit :<br>
</div>
<blockquote
cite="mid:1965324555.1600715.1517060081350@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 Respected <g class="gr_ gr_52 gr-alert gr_spell
gr_inline_cards gr_run_anim ContextualSpelling ins-del
multiReplace" id="52" data-gr-id="52">Xavaier</g> Sir</div>
<div>Thank you very much for detailed explanation.</div>
<div>My system is not having any d-d interaction (no TM
element) so I do not think I should go for DFT+U, Onsite
Hybrid functional and Full hybrid calculations!</div>
<div><br>
</div>
<div>With TB-mBJ it is showing a band gap. The VBM is widely
dispersed, flat for a wide range, near the VBM. So this is a
semiconductor.<br>
</div>
<div><br>
</div>
<div>As we can not relax the structure using mBJ so there is
no way to use it for the phonopy purpose (phonon bands).</div>
<div><br>
</div>
<div>Due to lack of good computational facilities, I want to
avoid hybrid calculation which will never finish if I go for
Phonopy.</div>
<div><br>
</div>
<div>What I see it, I use the combination of <g class="gr_
gr_94 gr-alert gr_spell gr_inline_cards gr_run_anim
ContextualSpelling ins-del multiReplace" id="94"
data-gr-id="94">tolf</g> and -<g class="gr_ gr_98 gr-alert
gr_spell gr_inline_cards gr_run_anim ContextualSpelling
ins-del multiReplace" id="98" data-gr-id="98">fc</g> such
that it gives minimum forces. But I am sure the forces will
not be less than 2mRy/Bohr. Again this process I see a
contradiction with Peter Sir's statement: forces should be
less than 1mRy/<g class="gr_ gr_509 gr-alert gr_spell
gr_inline_cards gr_run_anim ContextualSpelling ins-del
multiReplace" id="509" data-gr-id="509">bohr</g> for
phonon calculations and which I will not be having!!</div>
<div> </div>
<div>How much the ~2-3mRy/<g class="gr_ gr_921 gr-alert
gr_spell gr_inline_cards gr_run_anim ContextualSpelling
ins-del multiReplace" id="921" data-gr-id="921">bohr</g>
forces on the atom affects the phonon band structure?</div>
<div>can I proceed for phonon bands with the structure having
forces ~2-3 <g class="gr_ gr_1375 gr-alert gr_spell
gr_inline_cards gr_run_anim ContextualSpelling ins-del
multiReplace" id="1375" data-gr-id="1375">mRy</g>/Bohr?</div>
<div><br>
</div>
<div>Thank you very much!</div>
<div><br>
</div>
<div>Chin S.<br>
</div>
<div><br>
</div>
<div> </div>
<div><br>
</div>
<div><br>
</div>
<div> <br>
</div>
</div>
<div id="ydp1c4de612yahoo_quoted_7715263380"
class="ydp1c4de612yahoo_quoted">
<div style="font-family:'Helvetica Neue', Helvetica, Arial,
sans-serif;font-size:13px;color:#26282a;">
<div>On Saturday 27 January 2018, 6:31:35 PM IST, Xavier
Rocquefelte <a class="moz-txt-link-rfc2396E" href="mailto:xavier.rocquefelte@univ-rennes1.fr"><xavier.rocquefelte@univ-rennes1.fr></a>
wrote:</div>
<div><br>
</div>
<div><br>
</div>
<div>
<div id="ydp1c4de612yiv1933857513">
<div>
<p>Dear Chin S. <br clear="none">
</p>
<p>Your system is metallic from the point of view of
DFT which is not a surprise. <br clear="none">
</p>
<p>In your last calculation, which is the more
accurate you simply catch this fact ... In other <g
class="gr_ gr_68 gr-alert gr_gramm gr_inline_cards
gr_disable_anim_appear Punctuation only-ins
replaceWithoutSep" id="68" data-gr-id="68">words</g>
in your previous <g class="gr_ gr_69 gr-alert
gr_gramm gr_inline_cards gr_disable_anim_appear
Punctuation only-ins replaceWithoutSep" id="69"
data-gr-id="69">calculations</g> you had 0.1 eV
gap due to <g class="gr_ gr_67 gr-alert gr_gramm
gr_inline_cards gr_disable_anim_appear Grammar
multiReplace" id="67" data-gr-id="67">less</g> <g
class="gr_ gr_51 gr-alert gr_spell gr_inline_cards
gr_disable_anim_appear ContextualSpelling ins-del
multiReplace" id="51" data-gr-id="51">kpoints</g>
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 clear="none">
</p>
<p>Depending on the system you will have to consider
methods going beyond DFT, which in WIEN2k could be
based on: <br clear="none">
</p>
<p>- DFT+U</p>
<p>- Onsite Hybrid functional</p>
<p>- Full hybrid <br clear="none">
</p>
<p>- TB-mBJ potential</p>
<p>If your band gap is based on charge transfer
transitions you cannot <g class="gr_ gr_59 gr-alert
gr_gramm gr_inline_cards gr_disable_anim_appear
Grammar multiReplace" id="59" data-gr-id="59">used</g>
DFT+U and onsite-hybrid. <br clear="none">
Thus the less expensive approach will be TB-mBJ
potential which will give the band gap but not the
forces. <br clear="none">
</p>
<p>Thus only one option remains which is <g
class="gr_ gr_46 gr-alert gr_gramm gr_inline_cards
gr_disable_anim_appear Grammar only-ins
doubleReplace replaceWithoutSep" id="46"
data-gr-id="46">full</g> hybrid. <br clear="none">
</p>
<p>If your system is based on d-d <g class="gr_ gr_56
gr-alert gr_gramm gr_inline_cards
gr_disable_anim_appear Punctuation only-del
replaceWithoutSep" id="56" data-gr-id="56">transitions,</g>
or highly correlated states, then you can <g
class="gr_ gr_55 gr-alert gr_gramm gr_inline_cards
gr_disable_anim_appear Grammar multiReplace"
id="55" data-gr-id="55">used</g> DFT+U or
Onsite-hybrid. <br clear="none">
</p>
<p>Hope it will help you. <br clear="none">
</p>
<p>Cheers</p>
<p>Xavier<br clear="none">
</p>
<p><br clear="none">
</p>
<div class="ydp1c4de612yiv1933857513moz-cite-prefix">Le
27/01/2018 à 12:28, chin Sabsu a écrit :<br
clear="none">
</div>
<blockquote type="cite">
<div class="ydp1c4de612yiv1933857513yqt3890747714"
id="ydp1c4de612yiv1933857513yqt77601">
<div style="font-family: 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 clear="none">
</div>
<div>Below are my updates:</div>
<div><br clear="none">
</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 are different. NE varies
from 154 to 616(1x1x1 cell) to 4928 (2x2x2
cell).</div>
<div>So I will divide xxx numk by 4 and 32 in
1x1x1 and 2x2x2 supercell structure. Thanks
for this excellent recommendation!!!</div>
<div>For 2x2x2 supercell in phonopy
calculations, we need to go for mpi jobs for
certain cases!!<br clear="none">
</div>
<div><br clear="none">
</div>
<div>B. Now I have done some tests for my
cubic perovskite and below are my
observations:</div>
<div><br clear="none">
</div>
<div>B1. For tolf 5 and -fc1 I for FOR003 = ~4
mRy / bohr with band gap ~0.1 eV<br
clear="none">
</div>
<div>B2. For tolf 2 and - fc 0.1 forces are
almost same. and the band gap is still
~0.1ev<br clear="none">
</div>
<div><br clear="none">
</div>
<div>B3. Now to reduce the forces less then
0.1mRy/ bohr , I reduced the tolf to 0.5 and
- fc 0.1 - 0.01. I got forces at the desired
accurecy but the band gap vanished and the
system becomes metallic. The experimentally
reported band gap is 1.2eV<br clear="none">
</div>
<div>I used RKMAX 8, numk 2000, vxc 19.</div>
<div><br clear="none">
</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 clear="none">
</div>
<div>Kind regards</div>
<div><br clear="none">
</div>
<div>Chin S.</div>
<div><br clear="none">
</div>
<div> <br clear="none">
</div>
<div>For t olf<br clear="none">
</div>
<div><br clear="none">
</div>
</div>
</div>
</div>
<br clear="none">
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