<div dir="ltr">Dear S<span style="font-size:12.8px">tefano</span><div>thanks for your response.</div><div>Can you please guide me (1) Why vc-relax is not allowed in Q-E 5.4.0?</div><div>(2) How would the band gap be effected if I relax the cell without hybrid scheme and then calculate band gap with hybrid one?<br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, Jul 23, 2016 at 1:07 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 bgcolor="#FFFFFF" text="#000000">
<div>dear Muhammad Adnan Saqlain,<br>
<br>
gamma extrapolation is a way to deal with the ill defined value
of the exchange integral between wfcs at k and k+q in the limit of
q->0.<br>
if you use a truncated coulomb interaction that limit is not
ill defined.<br>
no need to use the gamma_extrapolation option<br>
best,<br>
stefano<br>
<br>
On 23/07/2016 10:00, Muhammad Adnan Saqlain wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Dear Prof Clavijo
<div>I am extremely sorry for my misleading title of the
calculation. Actually, It was a cubic structure consisting of
Cs, Pb and I. I deliberately did not put the atoms in the
calculation. more over I do not know why the algorithm for
cell movement was not copied it was however present in the
input file.</div>
<div><br>
</div>
<div>1. If I try these two options, the </div>
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<pre style="white-space:pre-wrap">vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
ecutvcut.</pre>
</blockquote>
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<div class="gmail_extra">the program says like this</div>
<div class="gmail_extra">
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%</div>
<div class="gmail_extra"> Error in routine system_checkin
(1):</div>
<div class="gmail_extra"> x_gamma_extrapolation cannot be
used with vcut</div>
<div class="gmail_extra"> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%</div>
<div><br>
</div>
</div>
<div class="gmail_extra">I have no idea how to fix it. Can you
suggest one??</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">2. I have now used Q-E 5.4.0, but this
version does not allow vc-relax option with hybrid one. why is
it so? How would the band gap be effected if I relax the cell
without hybrid scheme and then calculate band gap with hybrid
one?</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">3. About the ecutoff, I deliberately
used small one as these are just calculations not the real
one.</div>
<div class="gmail_extra">4. I have cubic system, may I try
q-grid like 1*2*3 or it has to be symmetric one?</div>
<div class="gmail_extra"> 5. Can you suggest more about hybrid
calculations?</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Fri, Jul 22, 2016 at 10:09 PM,
Josue Itsman Clavijo Penagos <span dir="ltr"><<a href="mailto:jiclavijop@unal.edu.co" target="_blank">jiclavijop@unal.edu.co</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
<div dir="ltr">Dear, Muhammad Adnan Saqlain, remember the
user documentation for <b style="font-size:13px">exxdiv_treatment</b>: <a name="m_1337774494978436259_m_4755999124063804085_exxdiv_treatment" style="color:rgb(0,0,0);font-family:arial,helvetica,sans-serif">
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<blockquote>
<pre>Specific for EXX. It selects the kind of approach to be used
for treating the Coulomb potential divergencies at small q vectors.
gygi-baldereschi : appropriate for cubic and <b>quasi-cubic supercells</b>
vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
ecutvcut.
none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE)</pre>
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</a><b>Besides that, </b>I<b> </b>have some
observations and suggestions for you based in the input
file you send, so you can realize why does QE is failing
when trying to simulate your system:
<div><br>
</div>
<div>1 - Check if you really need to apply smearing,
since this technique is intended to be useful for
metallic systems, and Anatase is cleary not a metallic
system, in fact, is more a Wide-gap or Insulator -type
system.<br>
<div><br>
</div>
<div>2 - You do want to perform a vc-relax
calculation, but nothing are specified in the cards
&IONS and &CELL. There is not cell relaxing
algorithm specified (BFGS? MD?)</div>
</div>
<div><br>
</div>
<div>3 - The card &ATOMIC_POSITIONS shows nothing:
No atoms, no cell to relax.</div>
<div><br>
</div>
<div>4 - In the card &SYSTEM , <b>ecutwfc = 40.</b>
This, in my humble opinion, a very poor cutoff for a
serious calculation. Do a ecutwfc convergence test
before attempt your system.</div>
<div><br>
</div>
<div>5 - Please take in account that a hybrid
calculation is VERY expensive in terms of
computational demand, so if you set up a vc-relax
calculation using hybrid PPS you must test if <b style="font-size:13px">nqx1 = 1, 2 or 3 really makes
a difference.</b></div>
<div><b style="font-size:13px"><br>
</b></div>
<div><b>6 - For some systems, input_dft=HSE is faster
than </b><b>input_dft = "PBE0". Check if that could
be your case.</b></div>
<div><b><br>
</b></div>
<div>By the way, are you sure Anatase has a cubic
crystal structure? Does XCrysden show the correct
structure for your input?</div>
<div><br>
</div>
<div><b>Best regards, </b></div>
<div><b><br>
</b></div>
<div class="gmail_extra"><br>
<div class="gmail_quote">Josué Clavijo, PhD.</div>
<div class="gmail_quote">Assistant Professor</div>
<div class="gmail_quote">Universidad Nacional de
Colombia</div>
<div class="gmail_quote">Departamento de Química</div>
</div>
</div>
<br>
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</blockquote>
</div>
<br>
<br clear="all"><span class="HOEnZb"><font color="#888888">
<div><br>
</div>
-- <br>
<div data-smartmail="gmail_signature">
<div dir="ltr">Best Regards
<div>Muhammad Adnan Saqlain
<div><br>
</div>
</div>
</div>
</div>
</font></span></div><span class="HOEnZb"><font color="#888888">
</font></span></div><span class="HOEnZb"><font color="#888888">
<br>
<fieldset></fieldset>
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<p><br>
</p>
</div>
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