[QE-users] Hubbard-U QE vs VASP

[Mahmoud Payami Shabestari]

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: mpayami at aeoi.org.ir
Phone: +98 (0)21 82066504
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From: Jhon Gonzalez <jhon.gonzalez at usm.cl>
To: "users at lists.quantum-espresso.org" <users at 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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