Dear Jhon, I would be quite surprised if there is a sign-convention mismatch between the two implementations. 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 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. 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. 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 using a dfpt implementation of linear response theory which is very efficient and user-friendly (PRB 103, 045141 (2021); PRB98, 085127 (2018)). 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 (PRB 102, 235159 (2020)). 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 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. 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 for more details).
Best regards, Matteo Il giorno lun 11 ott 2021 alle ore 01:37 Jhon Gonzalez <jhon.gonza...@usm.cl> ha scritto: > Hi, > > Perhaps this is a bit off-topic, there is an issue when comparing LDA+U > results in 2D-materials between Quantum-ESPRESSO and VASP. > For V2C monolayers, CrI3 mono- and bi-layers, the magnetic stability changes > and it is impossible to reproduce the results. > > For the V2C monolayer with U = 4 eV, while with quantum-ESPRESSO (US and > PBE), I find that the ground-state > (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 > is AF and the FM state is 1 eV above (in agreement with > dx.doi.org/10.1021/jp507336x). > > Following the discussion on the implementation of Hubbard's interaction: > https://lists.quantum-espresso.org/pipermail/users/2020-May/044521.html > There, it is suggested that in QE the Hubbard-U tends to decrease the gap, > while in VASP it tends to open it. > And inspired by the discussion > http://grandcentral.apam.columbia.edu:5555/tutorials/dft_procedures/linear_response_u/index.html > > there they mention an "empirically is a difference in sign convention". I > tried a VASP calculation with U = -4 eV, and I found an > FM GS-solution followed by an AF solution 0.3 eV above, following the QE > stability order. > > From my experience comparing QE results with CrI3 experiments, it seems > that QE uses the proper sign convention for the U term. > However, I do not have any evidence for this. > > I am currently exploring the use of hybrid functionals to address this > issue, is there an elegant way to settle this dispute? > > Best, > > > Jhon W. González > > Departamento de Física > Universidad Técnica Federico Santa María > VALPARAISO-CHILE > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list users@lists.quantum-espresso.org > https://lists.quantum-espresso.org/mailman/listinfo/users -- Matteo Cococcioni Department of Physics University of Pavia Via Bassi 6, I-27100 Pavia, Italy tel +39-0382-987485 e-mail matteo.cococci...@unipv.it <lucio.andre...@unipv.it>
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