[QE-users] Hubbard-U QE vs VASP

[Jhon Gonzalez]

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<http://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

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