<div dir="ltr"><div dir="ltr"><div>Dear Jhon,</div><div><br></div><div>I would be quite surprised if there is a sign-convention mismatch between the two implementations.</div><div>Please keep in mind that, even if you use the same type of pseudootentials, there is no guarantee that the same U should lead to the</div><div>same result (actually this is not the case most often). The value of U depends on all the details of the calculations and of the pseudopotnetial.</div><div>Of course, It would be interesting to compare the two codes on exactly
the same pseudopotential but I am afraid this is not (yet) possible.</div><div>If you want to compute it (which I recommend) please consider using the hp.x code (now part of the QE distribution) that allows you to determine its value</div><div>using a dfpt implementation of linear response theory which is very efficient and user-friendly (PRB 103, 045141 (2021); PRB98, 085127 (2018)). </div><div>Another thing I recommend to use with QE is orthogonalized atomic orbitals (U_projection_type = 'ortho-atomic') for which the code now has forces and stresses</div><div>(PRB 102, 235159 (2020)). <br></div><div>Please keep in mind also (and pehaps this makes up for most of the differences you observe) that VASP uses the the projectors of the seudopotentials (of PAW type</div><div>mostly) to define the atomic occupations then used in the Hubbard correction. In QE atomic wavefunctions are instead mostly used to project Kohn-Sham states on.</div><div>If you want a stricter comparison between the two perhaps you should use U_projection_type = 'pseudo' in QE (use PPs containing wavefunctions - see INPUT_PW.txt <br></div><div>for more details). <br></div><div><br></div><div>Best regards,<br></div><div><br></div><div>Matteo</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Il giorno lun 11 ott 2021 alle ore 01:37 Jhon Gonzalez <<a href="mailto:jhon.gonzalez@usm.cl">jhon.gonzalez@usm.cl</a>> ha scritto:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<div>Hi,</div>
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<div><span style="color:rgb(0,0,0)">Perhaps this is a bit off-topic,
</span><font color="#000000"><span>there is an issue when comparing LDA+U results in 2D-materials between Quantum-ESPRESSO and VASP.</span></font></div>
<div>For V2C monolayers, CrI3 mono- and bi-layers, the magnetic <span style="color:rgb(0,0,0)">stability </span>changes and it is impossible to reproduce the results.</div>
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<div>For the V2C monolayer with U = 4 eV, while with quantum-ESPRESSO (US and PBE), I find that the ground-state </div>
<div>(GS) solution is FM and the AF solution is about 1 eV above; with VASP U=4 eV (LDATYPE=2), I find that the GS solution </div>
<div>is AF and the FM state is 1 eV above (in agreement with <a href="http://dx.doi.org/10.1021/jp507336x" target="_blank">
dx.doi.org/10.1021/jp507336x</a>). </div>
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<div style="color:rgb(0,0,0)">Following the discussion on the implementation of Hubbard's interaction: <a href="https://lists.quantum-espresso.org/pipermail/users/2020-May/044521.html" target="_blank">https://lists.quantum-espresso.org/pipermail/users/2020-May/044521.html</a></div>
<div style="color:rgb(0,0,0)">There, it is suggested that in QE the Hubbard-U tends to decrease the gap, while in VASP it tends to open it.</div>
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<div>And inspired by the discussion <a href="http://grandcentral.apam.columbia.edu:5555/tutorials/dft_procedures/linear_response_u/index.html" target="_blank">
http://grandcentral.apam.columbia.edu:5555/tutorials/dft_procedures/linear_response_u/index.html</a> </div>
<div>there they mention an "empirically is a difference in sign convention". I tried a VASP calculation with U = -4 eV, and I found an </div>
<div>FM GS-solution followed by an AF solution 0.3 eV above, following the QE stability order.</div>
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<div>From my experience comparing QE results with CrI3 experiments, it seems that QE uses the proper sign convention for the U term. </div>
<div>However, I do not have any evidence for this.</div>
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<div>I am currently exploring the use of hybrid functionals to address this issue, is there an elegant way to settle this dispute?</div>
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<div>Best,</div>
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<div>Jhon W. González<br>
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Departamento de Física<br>
Universidad Técnica Federico Santa María<br>
VALPARAISO-CHILE</div>
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Quantum ESPRESSO is supported by MaX (<a href="http://www.max-centre.eu" rel="noreferrer" target="_blank">www.max-centre.eu</a>)<br>
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<a href="https://lists.quantum-espresso.org/mailman/listinfo/users" rel="noreferrer" target="_blank">https://lists.quantum-espresso.org/mailman/listinfo/users</a></blockquote></div><br clear="all"><br>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div>Matteo Cococcioni<br></div><div>Department of Physics<br></div>University of Pavia<br>Via Bassi 6, I-27100 Pavia, Italy<br>tel +39-0382-987485<br><div>e-mail <a href="mailto:lucio.andreani@unipv.it" target="_blank">matteo.cococcioni@unipv.it</a></div></div></div></div></div></div></div></div>