<div dir="ltr"><div class="gmail_default" style="font-size:large">Dear QE Users,<br></div><div class="gmail_quote"><div dir="ltr"><div style="font-size:large"><br></div><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><div style="font-size:large"><div class="gmail_default" style="font-size:large">I sincerely apologize for this long email. </div><br></div><div style="font-size:large"><br></div><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></div></div></div><blockquote style="margin:0 0 0 40px;border:none;padding:0px"><blockquote style="margin:0 0 0 40px;border:none;padding:0px"><div class="gmail_quote"><div dir="ltr"><div style="font-size:large"><div><div class="gmail_default" style="font-size:large">Supporting information for this email:</div></div></div></div></div></blockquote></blockquote><div class="gmail_quote"><div dir="ltr"><div style="font-size:large"><div class="gmail_default" style="font-size:large"><br></div><div class="gmail_default" style="font-size:large"><b><span class="gmail_default"></span>Combinations of my PPs:</b></div><br></div><div style="font-size:large">Set-1 (ecutwfc/ecutrho = 40/320Ry)<br></div><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></div><div style="font-size:large"><br></div><div style="font-size:large"><br></div><div style="font-size:large"><br></div><div style="font-size:large">Thank you very much for having patience while going through this detailed email.</div><div style="font-size:large"><br></div><div style="font-size:large">I look forward to hearing from you.<br></div><div style="font-size:large"><br></div><div style="font-size:large"><br></div><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></div><div style="font-size:large"><br></div><div style="font-size:large"><br></div></div>
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