Hi. DFT+U results in meta-stable states and careful analysis is needed for determining the true GS. Please look at the paper : https://arxiv.org/pdf/2108.12758.pdf which maybe useful. HTH
Mahmoud Payami NSTRI, AEOI, Tehran, Iran Email: mpay...@aeoi.org.ir Phone: +98 (0)21 82066504 -------------------------------------------------------- From: Jhon Gonzalez <jhon.gonza...@usm.cl> To: "users@lists.quantum-espresso.org" <users@lists.quantum-espresso.org> Date: Sun, 10 Oct 2021 23:36:57 +0000 Subject: [QE-users] Hubbard-U QE vs VASP 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,
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