<p dir="ltr">I think the problem might be related with iron ultrasoft pseudopotential.</p>
<p dir="ltr">As in page 40 of this pdf :</p>
<p dir="ltr"><a href="http://www.vasp.at/vasp-workshop/slides/pseudopp2.pdf">http://www.vasp.at/vasp-workshop/slides/pseudopp2.pdf</a></p>
<p dir="ltr">Low-spin case (NM) is okay. But for high-spin iron, energies are too different.</p>
<p dir="ltr">VASP use PAW potential. So you should switch to PAW with QE.</p>
<p dir="ltr">Hope this helps.</p>
<div class="gmail_quot<blockquote class=" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Dear Matteo,<div>thanks a lot for the reply.</div><div>I tried also using occupations="smearing" but the situation is the same. I get a difference of 0.3 electrons between the iron atom Fe1 and the other three Fe2.</div>
<div>Is there anything else that I can try? Could this behaviour due to the differences between VASP (that you used in the refererence article) and Quantum Espresso?</div><div>Best regards,</div><div>Mauro.</div><div><br>
</div><div class="gmail_extra">
<br><br><div class="gmail_quote">2014-06-06 16:55 GMT+02:00 Matteo Cococcioni <span dir="ltr"><<a href="mailto:matteo@umn.edu" target="_blank">matteo@umn.edu</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr"><div><div><div><br></div>Dear Mauro,<br><br></div>one thing I notice is that you are using occupation fixed. is there a reason for that? this, I think, might actually cause the result you are not happy about.<br>
<br></div>Matteo<br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Jun 6, 2014 at 4:39 PM, Mauro Sgroi <span dir="ltr"><<a href="mailto:maurofrancesco.sgroi@gmail.com" target="_blank">maurofrancesco.sgroi@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Dear all,<div>I'm trying to study the phase separation in LixFePO4 using DFT+U.</div><div>The reference article that I'm using is PRB 69, 201101 (R) 2004, "Phase separation in LixFePO4 induced by correlation effects, Zhou et al.</div>
<div><br></div><div>The authors compare, using VASP, standard DFT with DFT+U and obtain the correct description of the material with the latter approach. In particular they found that is possible to describe the formation of two type of ion, Fe2+ and Fe3+, according to to the different position in the unit cell in the partially lithiated structures. With GGA all Fe ions have the same occupancies, regardless the position in the cell and the fact that they are more or less near a lithium ion.</div>
<div>To obtain this result with DFT+U they had to force the breaking of the symmetry of the structure and, I imagine, they set the initial occupations in some way to force the desired electronic configuration.<br></div><div>
<br></div><div>I'm trying to do the same, differentiating the Fe atoms, breaking the symmetry and using starting_ns_eigenvalue to force the initial occupations. </div><div>My problem is that at the end of the calculation I got always the same occupations on the 4 Fe atoms in the structure (more or less, the difference could be 0.3 electrons).</div>
<div><br></div><div>I'm using lda_plus_u_kind=0, but also using the other approach was not beneficial.</div><div><br></div><div>My input file is below.</div><div>Have you any suggestion?</div><div><br></div><div>Thanks a lot in advance and best regards,</div>
<div>Mauro Sgroi.</div><div><br></div><div><div>&control</div><div> calculation='scf',</div><div> pseudo_dir = "/usr2/sgroi/DATABASE/ESPRESSO",</div><div> prefix='lifepo4_scfU',</div>
<div> outdir='/home/dati/espresso/temp',</div><div> /</div><div> &system</div><div> ibrav=8, celldm(1)=19.748515, celldm(2)=0.586193, celldm(3)=0.441599, nat=27, ntyp=5, nosym=.true.</div><div> ecutwfc=40, ecutrho=400, nbnd=130, occupations='fixed', nspin=2, tot_magnetization=17, </div>
<div> lda_plus_u=.true., Hubbard_U(2)=4., Hubbard_U(3)=4.475,</div><div> starting_ns_eigenvalue(5,2,2)=0,</div><div> starting_ns_eigenvalue(4,2,2)=0,</div><div> starting_ns_eigenvalue(3,2,2)=0,</div><div> starting_ns_eigenvalue(2,2,2)=0,</div>
<div> starting_ns_eigenvalue(1,2,2)=0,</div><div> starting_ns_eigenvalue(5,2,3)=1,</div><div> starting_ns_eigenvalue(4,2,3)=0,</div><div> starting_ns_eigenvalue(3,2,3)=0,</div><div> starting_ns_eigenvalue(2,2,3)=0,</div>
<div> starting_ns_eigenvalue(1,2,3)=0</div><div> /</div><div> &electrons</div><div> conv_thr=1.0d-8, electron_maxstep=100, mixing_beta=0.5</div><div> /</div><div><br></div><div>ATOMIC_SPECIES</div><div> Li 6.941 Li.pbe-s-van_ak.UPF</div>
<div> Fe1 55.847 Fe.pbe-sp-van_ak.UPF</div><div> Fe2 55.847 Fe.pbe-sp-van_ak.UPF</div><div> P 15.9994 P.pbe-van_ak.UPF</div><div> O 30.9737 O.pbe-van_ak.UPF</div><div><br></div><div>ATOMIC_POSITIONS {crystal}</div><div>
Fe1 0.<a href="tel:281537138%20%C2%A0%200" value="+12815371380" target="_blank">281537138 0</a>.250000000 0.981851206 1 0 1</div><div>P 0.103893879 0.250000000 0.415586970 1 0 1</div><div>
O 0.119764467 0.250000000 0.744164738 1 0 1</div><div>O 0.447356144 0.250000000 0.201257756 1 0 1</div>
<div>O 0.187375840 0.060350405 0.283173864</div><div>Li 0.500000000 0.000000000 0.500000000 0 0 0</div><div>Fe2 0.211199573 0.750000000 0.474632077 1 0 1</div><div>P 0.405092969 0.750000000 0.922566801 1 0 1</div>
<div>O 0.401164833 0.750000000 0.251505445 1 0 1</div><div>O 0.041727760 0.750000000 0.686207216 1 0 1</div><div>O 0.336134397 0.<a href="tel:956851552%20%C2%A0%200" value="+19568515520" target="_blank">956851552 0</a>.790300073</div>
<div>Li 0.000000000 0.500000000 0.000000000 0 0 0</div>
<div>Fe2 0.<a href="tel:719627852%20%C2%A0%200" value="+17196278520" target="_blank">719627852 0</a>.750000000 0.020422522 1 0 1</div><div>P 0.<a href="tel:902369089%20%C2%A0%200" value="+19023690890" target="_blank">902369089 0</a>.750000000 0.575773635 1 0 1</div>
<div>O 0.896492242 0.750000000 0.246982466 1 0 1</div><div>
O 0.<a href="tel:540334658%20%C2%A0%200" value="+15403346580" target="_blank">540334658 0</a>.750000000 0.790913565 1 0 1</div><div>O 0.840097513 0.<a href="tel:539754373%20%C2%A0%200" value="+15397543730" target="_blank">539754373 0</a>.720678002</div>
<div>Li 0.500000000 0.500000000 0.500000000 0 0 0</div><div>Fe2 0.<a href="tel:786894270%20%C2%A0%200" value="+17868942700" target="_blank">786894270 0</a>.250000000 0.525238732 1 0 1</div>
<div>P 0.588956858 0.250000000 0.078832190 1 0 1</div><div>O 0.587126133 0.250000000 0.749458661 1 0 1</div><div>O 0.966454798 0.250000000 0.315230191 1 0 1</div><div>
O 0.654364669 0.453679217 0.216461848</div><div>O 0.822813149 0.944845411 0.700568536</div><div>O 0.653714964 0.047069624 0.216100948</div><div>O 0.172021112 0.453011228 0.263457462</div>
<div>O 0.335493673 0.543326856 0.788919121</div><div><br></div><div>K_POINTS {automatic}</div></div><div>2 4 8 1 1 1</div><div><br></div></div>
<br>_______________________________________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a><br>
<a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br></blockquote></div><br></div>
<br>_______________________________________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a><br>
<a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br></blockquote></div><br></div></div>
<br>_______________________________________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
<a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br></div>