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<span>Hi, Dear Gui Wei,
</span></div><div><span><br></span></div><div><span>Using the PBE functional, the lattice constant of bcc Fe is supposed to be smaller than experimental value.</span></div><div><span>Please take a look at </span><a href="https://molmod.ugent.be/deltacodesdft." _src="https://molmod.ugent.be/deltacodesdft." style="line-height: 1.6;">https://molmod.ugent.be/deltacodesdft.</a> </div><div>Wien2K gives 2.831 A. PSlib and GBRV give some value around 2.834.</div><div><br></div><div>And, PBE is one of the best functionals on bcc Fe.</div><div><br></div><div><br></div><div><span>As Stefano suggests, you might need to increase somehow the plane wave cutoff, though. (to reproduce other properties correctly) (and as well as the k-points)</span></div><div><span><br></span></div>
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<span>Yi Wang
</span></div><div><span>Tsinghua University</span></div>
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<div style="font-size:12px;line-height:1.5;word-break:break-all;margin-left:10px;margin-right:10px">On <span class="mail-date">12/25/2018 18:02</span>，<a class="mail-to" style="text-decoration:none;color:#2a83f2;" href="mailto:degironc@sissa.it">Stefano de Gironcoli<degironc@sissa.it></a> wrote： </div>
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<p><tt>cutoff might be too small for a reliable computation of the
stress.</tt></p>
<p><tt>other than that I see no big issue in your input</tt></p>
<p><tt>stefano</tt><br>
</p>
<div class="moz-cite-prefix">On 25/12/18 04:35, Gui Wei wrote:<br>
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<blockquote type="cite" cite="mid:668a2fad.15e1.167e36e740d.Coremail.201707021019@cqu.edu.cn">
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<div><font face="Times New Roman">Hi,</font></div>
<div><font face="Times New Roman"><span style="white-space:pre"> </span>When
optimizing the lattice constant of bcc Fe,the result is
a=2.830A， which is in disagreement with experimentally derived
structural parameter a=2.863A.Could someone give me some
advice?</font></div>
<div><font face="Times New Roman"><br>
</font></div>
<div><font face="Times New Roman">&CONTROL</font></div>
<div><font face="Times New Roman"> calculation = 'vc-relax'</font></div>
<div><font face="Times New Roman"> prefix='Fe1',</font></div>
<div><font face="Times New Roman"> pseudo_dir =
'/public/home/duan1/gw2/pseudo/',</font></div>
<div><font face="Times New Roman">
outdir='/public/home/duan1/gw2/tempdir/'</font></div>
<div><font face="Times New Roman"> tprnfor = .true.</font></div>
<div><font face="Times New Roman"> tstress = .true.</font></div>
<div><font face="Times New Roman">/</font></div>
<div><font face="Times New Roman">&SYSTEM</font></div>
<div><font face="Times New Roman"> ibrav= 1, </font></div>
<div><font face="Times New Roman"> A=2.8664</font></div>
<div><font face="Times New Roman"> nat= 2 </font></div>
<div><font face="Times New Roman"> ntyp= 1</font></div>
<div><font face="Times New Roman"> occupations='smearing',</font></div>
<div><font face="Times New Roman"> smearing='mp',</font></div>
<div><font face="Times New Roman"> degauss=0.02,</font></div>
<div><font face="Times New Roman"> ecutwfc =37</font></div>
<div><font face="Times New Roman"> ecutrho =240</font></div>
<div><font face="Times New Roman"> nspin = 2</font></div>
<div><font face="Times New Roman"> starting_magnetization(1) =
0.4</font></div>
<div><font face="Times New Roman">/</font></div>
<div><font face="Times New Roman">&ELECTRONS</font></div>
<div><font face="Times New Roman"> conv_thr = 1.0d-8</font></div>
<div><font face="Times New Roman"> mixing_beta = 0.7</font></div>
<div><font face="Times New Roman">/</font></div>
<div><font face="Times New Roman">&IONS</font></div>
<div><font face="Times New Roman"> ion_dynamics = 'bfgs'</font></div>
<div><font face="Times New Roman">/</font></div>
<div><font face="Times New Roman">&CELL</font></div>
<div><font face="Times New Roman"> cell_dynamics = 'bfgs' </font></div>
<div><font face="Times New Roman">/ </font></div>
<div><font face="Times New Roman">ATOMIC_SPECIES</font></div>
<div><font face="Times New Roman">Fe 55.847
Fe.pbe-n-kjpaw_psl.0.2.4.UPF</font></div>
<div><font face="Times New Roman">ATOMIC_POSITIONS crystal</font></div>
<div><font face="Times New Roman"> Fe 0.0000000000000000
0.0000000000000000 0.0000000000000000</font></div>
<div><font face="Times New Roman"> Fe 0.5000000000000001
0.5000000000000001 0.5000000000000001</font></div>
<div><font face="Times New Roman">K_POINTS automatic</font></div>
<div><font face="Times New Roman">8 8 8 0 0 0</font></div>
<div><br>
</div>
<div><font face="Times New Roman">The result:</font></div>
<div><font face="Times New Roman">
<div> CELL_PARAMETERS (alat= 5.41671099)</div>
</font>
<div><font face="Times New Roman"> 0.987418499 0.000000000
0.000000000</font></div>
<div><font face="Times New Roman"> 0.000000000 0.987418499
0.000000000</font></div>
<div><font face="Times New Roman"> 0.000000000 0.000000000
0.987418499</font></div>
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</font></div>
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</font></div>
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<div><font size="3" face="Times New Roman">Gui Wei</font></div>
<div><font size="3" face="Times New Roman">School of Mechanical
Engineering，Chongqing University, China</font></div>
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