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<p><span style="font-size: 12pt; font-family: Arial, Helvetica, sans-serif; color: rgb(0, 0, 0);">Dear
</span><font size="4"><font size="4"><span style="font-size: 12pt; font-family: Arial, Helvetica, sans-serif; color: rgb(0, 0, 0);">K C Bhamu</span></font></font><span style="font-size: 12pt; font-family: Arial, Helvetica, sans-serif; color: rgb(0, 0, 0);">,</span></p>
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<p><font size="4"><font size="4">> Do you think my input file (see below) has any issues? I have defined all tetra-Fe sites dn-spin and all octahedra Fe sites up-spin.
<br>
</font></font></p>
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<p>I recommend to check with the QE input generator: <a href="https://www.materialscloud.org/work/tools/qeinputgenerator" class="OWAAutoLink" id="LPlnk63756" previewremoved="true">
https://www.materialscloud.org/work/tools/qeinputgenerator</a></p>
<p><br>
</p>
<p><font size="4"><font size="4">> What other things I should take care of to reproduce the band gap (0.14 eV to 0.3 eV)?</font></font><br>
</p>
<p><br>
</p>
<p>I never studied this system but I can give general comments:</p>
<p>- you can try to determine Hubbard parameters using the HP code of QE<br>
</p>
<p>- you can try to use "ortho-atomic" Hubbard projectors instead of "atomic" (<span>U_projection_type</span>):
<a href="https://www.mdpi.com/2076-3417/11/5/2395" class="OWAAutoLink" id="LPlnk854714" previewremoved="true">
https://www.mdpi.com/2076-3417/11/5/2395</a></p>
<p>- maybe try DFT+U+V? <a href="https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.5.104402" class="OWAAutoLink" id="LPlnk263762" previewremoved="true">
https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.5.104402</a> (see Fig. 6) Tutorial:
<a href="https://www.youtube.com/watch?v=WSABAqPWNH0&t=5s" class="OWAAutoLink" id="LPlnk318874" previewremoved="true">
https://www.youtube.com/watch?v=WSABAqPWNH0&t=5s</a></p>
<p><br>
</p>
<p><font size="4"><font size="4">> In the </font><a href="https://iopscience.iop.org/article/10.1088/1468-6996/15/4/044202" target="_blank" rel="noopener noreferrer"><font size="4">research paper [3]</font></a><font size="4">, the authors used VASP and the
valence configuration for the Fe atom was taken as 3d64s1. I could not find any PP from the list I mention below which has this configuration. Does this may be an issue? </font>If anyone has PP of Fe with 3d64s1 configuration, please provide me.</font><br>
</p>
<p><br>
</p>
<p>Check SSSP: <a href="https://www.materialscloud.org/discover/sssp/table/efficiency" class="OWAAutoLink" id="LPlnk506580" previewremoved="true">
https://www.materialscloud.org/discover/sssp/table/efficiency</a></p>
<p><br>
</p>
<p>HTH</p>
<p><br>
</p>
<p>Iurii<br>
</p>
<p><br>
</p>
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<span style="font-family:Cambria,Georgia,serif">Dr. Iurii TIMROV</span><br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of Dr. K. C. Bhamu <kcbhamu85@gmail.com><br>
<b>Sent:</b> Monday, November 15, 2021 11:47:16 AM<br>
<b>To:</b> Quantum Espresso users Forum<br>
<b>Subject:</b> [QE-users] Need some suggestion regarding the band gap issue of Fe3O4</font>
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<div class="gmail_default" style="font-size:large">Dear QE Users,<br>
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<div style="font-size:large">This email may be large for you<span class="gmail_default" style="font-size:large"> all </span>as I am trying to put all the information so that I do not miss any information in your response. </div>
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<div class="gmail_default" style="font-size:large">I sincerely apologize for this long email.
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<div style="font-size:large">I am dealing with <span class="gmail_default" style="font-size:large">
ferrimagnetic </span>Fe3O4<span class="gmail_default" style="font-size:large"> (with QE6.6)</span> and trying to reproduce its band gap.<span class="gmail_default" style="font-size:large"> In the literature, its experimental band gap was reported to be in the
range of 0.14-0.3eV, <a href="https://aip.scitation.org/doi/10.1063/1.5138941">Table SI-1 [1]</a> for the up-spin state. For Fe3O4 nanoparticles, the band gap is reported ~2eV.</span></div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large">I have tried with all available PPs (mentioned below in different sets) and U values from 1eV to 7eV<span class="gmail_default" style="font-size:large">. </span>At lower U (<span class="gmail_default">=</span>1-2eV), I am getting
this system a direct band-gap half-metal (a gap is opened in the spin-up channel) and with increasing the U value, the direct band-gap (<span class="gmail_default">=</span>~1eV) nature changes to the indirect (<span class="gmail_default">=</span>~2eV) band
gap. At U=7eV with the rrkjus PPs, it showed a metallic character. </div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large">I have also carried out the band structure, by keeping the lattice parameters fixed at experimental values and only relaxing ionic position, with <span class="gmail_default" style="font-size:large">varying</span> U-values. But still,
the nature of the bang-gap is similar to what I just mentioned above(<span class="gmail_default" style="font-size:large">band gap varies from
</span>~1eV to ~2eV with U=1eV to 7eV, respectively).</div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large">The lattice parameters, magnetic moments, and the charge on Fe_tet and Fe_oct sites I am getting reasonably in accordance with the
<a href="https://aip.scitation.org/doi/10.1063/1.5138941">Table SI-1</a><span class="gmail_default" style="font-size:large">.</span></div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large">A sample of my input file is also shown below (the only PPs are different with respective cutoffs).</div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large">Information collected from other research papers:</div>
<div style="font-size:large">1. <span class="gmail_default" style="font-size:large">
</span><a href="https://www.sciencedirect.com/science/article/abs/pii/S0039602812000544" target="_blank">See [2]</a> (In section 3.1. Bulk Fe3O4: 0.33 eV band gap with VASP with U=3.8eV ). </div>
<div style="font-size:large">2. <span class="gmail_default" style="font-size:large">
</span><a href="https://iopscience.iop.org/article/10.1088/1468-6996/15/4/044202" target="_blank">See [3]</a> <font color="#000000">(Page-4, bottom left para: 2.1 eV using VASP with U=4 eV). </font><font color="#ff0000" style="font-weight:bold">This paper
only shows the </font><font style="font-weight:bold" color="#0000ff">direct band-gap of</font><font style="font-weight:bold" color="#0000ff"> 2.1eV</font><font color="#ff0000" style="font-weight:bold">.</font></div>
<div style="font-size:large">
<div class="gmail_default" style="font-size:large"></div>
<div class="gmail_default" style="font-size:large">Based on my already finished calculations and the details that I have covered above, I have a few queries:</div>
</div>
<div style="font-size:large">
<ol>
<li><span class="gmail_default" style="font-size:large">Do you think my input file (see below) has any issues? I have defined all tetra-Fe sites dn-spin and all octahedra Fe sites up-spin. </span></li><li><span class="gmail_default" style="font-size:large">What other things I should take care of to reproduce the band gap (0.14 eV to 0.3 eV)?</span></li><li><span class="gmail_default" style="font-size:large">In the <a href="https://iopscience.iop.org/article/10.1088/1468-6996/15/4/044202">
research paper [3]</a>, the authors used VASP and the valence configuration for the Fe atom was taken as 3d64s1. I could not find any PP from the list I mention below which has this configuration. Does this may be an issue? </span>If anyone has PP of Fe with 3d64s1<span class="gmail_default">
configuration, please provide me.</span></li><li><span class="gmail_default" style="font-size:large">As mentioned in the<b> </b><a href="https://pubs.acs.org/doi/full/10.1021/acs.jpcc.7b09387" style="font-weight:400">research paper [4]</a><span style="font-weight:400">, the authors have mentioned that
"</span><span class="gmail_default" style="font-weight:400;font-family:georgia,serif"></span><span style="font-weight:400;font-family:georgia,serif"><font color="#000000">Our results show that, upon releasing the symmetry constraint on the density but not
on the geometry, charge disproportionation (Fe2+/Fe3+) is observed, resulting in a band gap of around 0.2 eV at the Fermi level.</font>" How can I release symmetry constrain on the density? I used nonsym=True also but the calculation was not converging in
this case. </span></span><b></b></li></ol>
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<div class="gmail_default" style="font-size:large">Supporting information for this email:</div>
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<div class="gmail_default" style="font-size:large"><b><span class="gmail_default"></span>Combinations of my PPs:</b></div>
<br>
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<div style="font-size:large">Set-1 (ecutwfc/ecutrho = 40/320Ry)<br>
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<div style="font-size:large">Fe.pbe-nd-rrkjus.UPF<br>
O.pbe-rrkjus.UPF<br>
</div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large">Set-2 (ecutwfc/ecutrho = 45/450Ry)</div>
<div style="font-size:large">Fe.pbe-sp-van_mit.UPF<br>
O.pbe-rrkjus.UPF<br>
</div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large"><b>Set-3 (ecutwfc/ecutrho = 65/785Ry) >> similar to yours</b></div>
<div style="font-size:large"><b>Fe.pbe-spn-rrkjus_psl.1.0.0.UPF<br>
O.pbe-n-rrkjus_psl.1.0.0.UPF</b><br>
</div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large">set-4 (ecutwfc/ecutrho = 64/782Ry)</div>
<div style="font-size:large">Fe.pbe-spn-kjpaw_psl.0.2.1.UPF<br>
O.pbe-n-kjpaw_psl.0.1.UPF<br>
</div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large"><b>QE input file:</b></div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large">&CONTROL<br>
calculation = '<span class="gmail_default" style="font-size:large">scf</span>'<br>
etot_conv_thr = 1.0000000000d-04<br>
forc_conv_thr = 1.0000000000d-03<br>
! disk_io = 'none'<br>
outdir = './tmp/'<br>
prefix = 'pwscf'<br>
pseudo_dir = '~/PPs/'<br>
<span class="gmail_default" style="font-size:large">!</span> tprnfor = .true.<br>
<span class="gmail_default" style="font-size:large">!</span> tstress = .true.<br>
! verbosity = 'high'<br>
/<br>
&SYSTEM<br>
degauss = 0.01<br>
ecutrho = 785<br>
ecutwfc = 65<br>
ibrav = 0<br>
nat = 56<br>
nosym = .false.<span class="gmail_default" style="font-size:large"> !! I have tried with .True. also but my calculations were not converging.
</span><br>
ntyp = 3<br>
occupations = 'smearing' , smearing = 'mp'<br>
starting_magnetization(1) = 1<br>
starting_magnetization(2) = -1<br>
nspin = 2<br>
lda_plus_u=.true.<br>
Hubbard_U(1)=X (tried 1eV to 7eV)<br>
Hubbard_U(2)=X (tried 1eV to 7eV)<br>
<br>
<br>
/<br>
&ELECTRONS<br>
conv_thr = 1.000000000d-6<br>
electron_maxstep = 200<br>
mixing_beta = 3.0000000000d-01<br>
/<br>
&IONS<br>
ion_dynamics = 'bfgs'<br>
/<br>
&CELL<br>
/<br>
<br>
ATOMIC_SPECIES<br>
Fe1 55.845 Fe.pbe-spn-rrkjus_psl.1.0.0.UPF<br>
Fe2 55.845 Fe.pbe-spn-rrkjus_psl.1.0.0.UPF<br>
O 15.9994 O.pbe-n-rrkjus_psl.1.0.0.UPF<br>
ATOMIC_POSITIONS crystal<br>
Fe1 0.6250000000 0.6250000000 0.6250000000 <br>
Fe1 0.6250000000 0.3750000000 0.3750000000 <br>
Fe1 0.3750000000 0.6250000000 0.3750000000 <br>
Fe1 0.3750000000 0.3750000000 0.6250000000 <br>
Fe1 0.6250000000 0.8750000000 0.8750000000 <br>
Fe1 0.8750000000 0.6250000000 0.8750000000 <br>
Fe1 0.8750000000 0.8750000000 0.6250000000 <br>
Fe1 0.6250000000 0.1250000000 0.1250000000 <br>
Fe1 0.1250000000 0.6250000000 0.1250000000 <br>
Fe1 0.1250000000 0.1250000000 0.6250000000 <br>
Fe1 0.1250000000 0.3750000000 0.8750000000 <br>
Fe1 0.1250000000 0.8750000000 0.3750000000 <br>
Fe1 0.3750000000 0.1250000000 0.8750000000 <br>
Fe1 0.8750000000 0.1250000000 0.3750000000 <br>
Fe1 0.3750000000 0.8750000000 0.1250000000 <br>
Fe1 0.8750000000 0.3750000000 0.1250000000 <br>
Fe2 0.0000000000 0.0000000000 0.0000000000 <br>
Fe2 0.2500000000 0.2500000000 0.2500000000 <br>
Fe2 0.0000000000 0.5000000000 0.5000000000 <br>
Fe2 0.5000000000 0.0000000000 0.5000000000 <br>
Fe2 0.5000000000 0.5000000000 0.0000000000 <br>
Fe2 0.2500000000 0.7500000000 0.7500000000 <br>
Fe2 0.7500000000 0.2500000000 0.7500000000 <br>
Fe2 0.7500000000 0.7500000000 0.2500000000 <br>
O 0.3750000000 0.3750000000 0.3750000000 <br>
O 0.3750000000 0.6250000000 0.6250000000 <br>
O 0.6250000000 0.3750000000 0.6250000000 <br>
O 0.6250000000 0.6250000000 0.3750000000 <br>
O 0.8750000000 0.8750000000 0.8750000000 <br>
O 0.8750000000 0.6250000000 0.6250000000 <br>
O 0.6250000000 0.8750000000 0.6250000000 <br>
O 0.6250000000 0.6250000000 0.8750000000 <br>
O 0.3750000000 0.8750000000 0.8750000000 <br>
O 0.8750000000 0.3750000000 0.8750000000 <br>
O 0.8750000000 0.8750000000 0.3750000000 <br>
O 0.3750000000 0.1250000000 0.1250000000 <br>
O 0.8750000000 0.6250000000 0.1250000000 <br>
O 0.8750000000 0.1250000000 0.6250000000 <br>
O 0.6250000000 0.8750000000 0.1250000000 <br>
O 0.1250000000 0.3750000000 0.1250000000 <br>
O 0.1250000000 0.8750000000 0.6250000000 <br>
O 0.6250000000 0.1250000000 0.8750000000 <br>
O 0.1250000000 0.6250000000 0.8750000000 <br>
O 0.1250000000 0.1250000000 0.3750000000 <br>
O 0.8750000000 0.3750000000 0.3750000000 <br>
O 0.3750000000 0.8750000000 0.3750000000 <br>
O 0.3750000000 0.3750000000 0.8750000000 <br>
O 0.8750000000 0.1250000000 0.1250000000 <br>
O 0.3750000000 0.6250000000 0.1250000000 <br>
O 0.3750000000 0.1250000000 0.6250000000 <br>
O 0.6250000000 0.3750000000 0.1250000000 <br>
O 0.1250000000 0.8750000000 0.1250000000 <br>
O 0.1250000000 0.3750000000 0.6250000000 <br>
O 0.6250000000 0.1250000000 0.3750000000 <br>
O 0.1250000000 0.6250000000 0.3750000000 <br>
O 0.1250000000 0.1250000000 0.8750000000<br>
K_POINTS automatic<br>
3 3 3 0 0 0<br>
CELL_PARAMETERS angstrom<br>
8.3840000000 0.0000000000 0.0000000000<br>
0.0000000000 8.3840000000 0.0000000000<br>
0.0000000000 0.0000000000 8.3840000000<br>
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<div style="font-size:large">Thank you very much for having patience while going through this detailed email.</div>
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<div style="font-size:large">I look forward to hearing from you.<br>
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<div style="font-size:large">Regards</div>
<div style="font-size:large"><br>
</div>
<div style="font-size:large">
<div class="gmail_default" style="font-size:large">K C Bhamu</div>
<div class="gmail_default" style="font-size:large">Postdoctoral Fellow</div>
<div class="gmail_default" style="font-size:large">School of Chemical Engineering</div>
<div class="gmail_default" style="font-size:large">University of Ulsan</div>
<div class="gmail_default" style="font-size:large">South Korea</div>
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