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<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">I would like to add a few words on the comments by Iurii:</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;"> </div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">Using the switch "U_projection='ortho_atomic' " had already been tested in my study of meta-stable states.</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">It does not alter the main arguments in my case; but what I had found was that using the normalized localized atomic orbitals slightly changes the electron densities and thereby slightly shifts the total energies of the GS and meta-stable states; but does not alter the hierarchy of the states.</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">I would like to thank Iurii for the reference provided. </div>
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<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;">Mahmoud Payami</div>
<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;">NSTRI, AEOI, Tehran, Iran</div>
<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;"> </div>
<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;">Email: mpayami@aeoi.org.ir</div>
<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;">Phone: +98 (0)21 82066504</div>
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<blockquote class="as91pFk8AX8sDPOUp66RUy8IoCRjefxNG8oLk8fg" style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">From: Iurii TIMROV via users <users@lists.quantum-espresso.org><br />
To: Quantum ESPRESSO users Forum <users@lists.quantum-espresso.org><br />
Date: Mon, 11 Oct 2021 08:41:59 +0000<br />
Subject: Re: [QE-users] Hubbard-U QE vs VASP<br />
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<div>Dear All,</div>
<div> </div>
<div>In addition to what Matteo explained, I would like to point your attention to the following article which is relevant (in my opinion) for this discussion (QE vs VASP): <a class="OWAAutoLink" href="https://aip.scitation.org/doi/10.1063/1.4945608" id="LPlnk273868" previewremoved="true"> https://aip.scitation.org/doi/10.1063/1.4945608</a></div>
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<div>Greetings,</div>
<div>Iurii</div>
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<div dir="ltr" id="divRplyFwdMsg"><font color="#000000" face="Calibri, sans-serif" style="font-size:11pt"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of Matteo Cococcioni <matteo.cococcioni@unipv.it><br />
<b>Sent:</b> Monday, October 11, 2021 10:22:08 AM<br />
<b>To:</b> Quantum ESPRESSO users Forum<br />
<b>Subject:</b> Re: [QE-users] Hubbard-U QE vs VASP</font>
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<div>Dear Jhon,</div>
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<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)).</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</div>
<div>for more details).</div>
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<div>Best regards,</div>
<div> </div>
<div>Matteo</div>
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<div class="gmail_attr" dir="ltr">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:</div>
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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>
<div> </div>
<div>
<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>
<div> </div>
<div>I am currently exploring the use of hybrid functionals to address this issue, is there an elegant way to settle this dispute?</div>
<div> </div>
<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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<div>Matteo Cococcioni</div>
<div>Department of Physics</div>
University of Pavia<br />
Via Bassi 6, I-27100 Pavia, Italy<br />
tel +39-0382-987485
<div>e-mail <a href="mailto:lucio.andreani@unipv.it" target="_blank">matteo.cococcioni@unipv.it</a></div>
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