[QE-users] Why my Hubbard parameter is so much bigger than what I find in the litterature?

Tue Feb 28 14:06:15 CET 2023

Dear Lorenzo,

With the U parameter that I got I checked the DOS and bandstructure. I noticed that the gap became more closer to the experimental value by shifting down the valence band maximum value.

But I`m always wondering if the U that I computed is correct (20 eV) as it differes too much from the ones listed in the litterature (5-6 eV).

------------------------------------------------------------
Salma NAIMI
PhD student - Mohamed 5 University-Rabat

________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Lorenzo Paulatto <lorenzo.paulatto at cnrs.fr>
Sent: Tuesday, February 28, 2023 1:34 PM
To: users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] Why my Hubbard parameter is so much bigger than what I find in the litterature?

On 2/28/23 13:22, NAIMI SALMA wrote:
Ah ok, I see.

So for the moment I have to take it from the litterature if i`m using a material with a closed-shell.

I would recommend you fit (or at least check) on some physical parameter, like the band gap. As the precise value of U depends on the reference wavefunctions, which depend on the pseudopotential, literature values are not transferable.

regards

------------------------------------------------------------
Salma NAIMI
PhD student - Mohamed 5 University-Rabat

________________________________
From: Iurii TIMROV <iurii.timrov at epfl.ch><mailto:iurii.timrov at epfl.ch>
Sent: Tuesday, February 28, 2023 1:16 PM
To: NAIMI SALMA <salma_naimi at um5.ac.ma><mailto:salma_naimi at um5.ac.ma>; Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org><mailto:users at lists.quantum-espresso.org>
Subject: Re: [QE-users] Why my Hubbard parameter is so much bigger than what I find in the litterature?

> Do I have to use occupations='fixed' instead of smearing just to compute the Hubbard parameter, or  in all the calculations that I perform on CuI ?

In all calculations

> So nowto compute the Hubbard parameter I have to run one scf calculation with occupations='fixed' then run hp.x , right?

Yes, but the U value will still be too large. So what I wanted to say previously is that I would not try to compute U using the HP code. It is a limitation of linear-response theory to compute U for closed-shell systems. We have some ideas how to overcome this issue, but it requires more testing and implementation in HP.

Iurii

--
Dr. Iurii TIMROV
Senior Research Scientist
Theory and Simulation of Materials (THEOS)
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: NAIMI SALMA <salma_naimi at um5.ac.ma><mailto:salma_naimi at um5.ac.ma>
Sent: Tuesday, February 28, 2023 1:12:36 PM
To: Iurii TIMROV; Quantum ESPRESSO users Forum
Subject: Re: [QE-users] Why my Hubbard parameter is so much bigger than what I find in the litterature?

Ok thank you.

My material is a p-type semiconductor. So nowto compute the Hubbard parameter I have to run one scf calculation with occupations='fixed' then run hp.x , right?

Do I have to use occupations='fixed' instead of smearing just to compute the Hubbard parameter, or  in all the calculations that I perform on CuI ?

-------------------------------------------------------
Salma NAIMI
PhD student - Mohamed 5 University-Rabat

________________________________
From: Iurii TIMROV <iurii.timrov at epfl.ch><mailto:iurii.timrov at epfl.ch>
Sent: Tuesday, February 28, 2023 1:03 PM
To: NAIMI SALMA <salma_naimi at um5.ac.ma><mailto:salma_naimi at um5.ac.ma>; Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org><mailto:users at lists.quantum-espresso.org>
Subject: Re: [QE-users] Why my Hubbard parameter is so much bigger than what I find in the litterature?

Ok, I see. That message was meant for magnetic insulators and now I understand why it was confusing for you. We will modify it. Since your system is nonmagnetic and insulating, do not use smearing (instead use occupations='fixed').

HTH

Iurii

--
Dr. Iurii TIMROV
Senior Research Scientist
Theory and Simulation of Materials (THEOS)
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: NAIMI SALMA <salma_naimi at um5.ac.ma><mailto:salma_naimi at um5.ac.ma>
Sent: Tuesday, February 28, 2023 12:56:54 PM
To: Iurii TIMROV; Quantum ESPRESSO users Forum
Subject: Re: [QE-users] Why my Hubbard parameter is so much bigger than what I find in the litterature?

Dear Iurii,

Actually in the first attempt  I had run just one scf calculation, but after running hp.x I got the following message in the output file:

      WARNING: The Fermi energy shift is zero or too big!
      This may happen in two cases:
      1. The DOS at the Fermi level is too small:
         DOS(E_Fermi) =   -0.3416E-35
         This means that most likely the system has a gap,
         and hence it should NOT be treated as a metal
         (otherwise numerical instabilities will appear).
      2. Numerical instabilities due to too low cutoff
         for hard pseudopotentials.

      Stopping...

      Solution: Try to use the 2-step scf procedure as in HP/example02

So based on that I followed HP/example02 then and ran the second scf calculation then hp.x

-------------------------------------------------------
Salma NAIMI
PhD student - Mohamed 5 University-Rabat

________________________________
From: users <users-bounces at lists.quantum-espresso.org><mailto:users-bounces at lists.quantum-espresso.org> on behalf of Iurii TIMROV via users <users at lists.quantum-espresso.org><mailto:users at lists.quantum-espresso.org>
Sent: Tuesday, February 28, 2023 12:44 PM
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org><mailto:users at lists.quantum-espresso.org>
Subject: Re: [QE-users] Why my Hubbard parameter is so much bigger than what I find in the litterature?

Dear Salma,

There is no need to run two SCF calculations in your case (it is only needed for magnetic insulators, see README in example02 of HP).

Cu is a problematic element for HP (linear response theory) because the 3d shell is full and in this case the approach is not suitable. For more details see J. Chem. Phys. 140, 121105 (2014).

HTH

Iurii

--
Dr. Iurii TIMROV
Senior Research Scientist
Theory and Simulation of Materials (THEOS)
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: users <users-bounces at lists.quantum-espresso.org><mailto:users-bounces at lists.quantum-espresso.org> on behalf of NAIMI SALMA <salma_naimi at um5.ac.ma><mailto:salma_naimi at um5.ac.ma>
Sent: Tuesday, February 28, 2023 12:29:27 PM
To: Quantum ESPRESSO users Forum
Subject: Re: [QE-users] Why my Hubbard parameter is so much bigger than what I find in the litterature?

Dear Giovanni,

You`ll find attached the input files of scf1, scf2 and hp that I used to compute the hubbard parameter.

Can you help me to know the exact error please!

-------------------------------------------------------
Salma NAIMI
PhD student - Mohamed 5 University-Rabat

________________________________
From: users <users-bounces at lists.quantum-espresso.org><mailto:users-bounces at lists.quantum-espresso.org> on behalf of Giovanni Cantele <giovanni.cantele at spin.cnr.it><mailto:giovanni.cantele at spin.cnr.it>
Sent: Tuesday, February 28, 2023 12:18 PM
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org><mailto:users at lists.quantum-espresso.org>
Subject: Re: [QE-users] Why my Hubbard parameter is so much bigger than what I find in the litterature?

Dear Salma,

hard to say without knowing which material and atomic species you're dealing with. Generally speaking, if people expect a 5-6 eV U and you find more than 3 times more, I would suspect that an error is somwhere in the simulations.
You should certainly check whether you used appropriate calculation parameters, e.g. BZ sampling, cutoff(s), and so on.

Giovanni
--

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it<mailto:giovanni.cantele at spin.cnr.it>
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: https://sites.google.com/view/giovanni-cantele/home

Il giorno mar 28 feb 2023 alle ore 12:04 NAIMI SALMA <salma_naimi at um5.ac.ma<mailto:salma_naimi at um5.ac.ma>> ha scritto:
Dear experts,
I'm working on inorganic p-type semiconductor using qe-7.0 . I want to use GGA+U, so I computed the U value by following the steps from the HP directory/example 02 for NiO (scf1 then scf2 then then hp) without including the magnetization because my material is not magnetic. My hubbard parameter was around 20 eV. While the used parameter for the same material in previous papers is around 5-6 eV ( Knowing that in previous papers they were extracting the U parameter from the litterature). The difference is big between their hubbard parameter and mine is that normal or did I do something wrong?

-------------------------------------------------------
Salma NAIMI
PhD student - Mohamed 5 University-Rabat

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The Quantum ESPRESSO community stands by the Ukrainian
people and expresses its concerns about the devastating
effects that the Russian military offensive has on their
country and on the free and peaceful scientific, cultural,
and economic cooperation amongst peoples
_______________________________________________
Quantum ESPRESSO is supported by MaX (www.max-centre.eu<http://www.max-centre.eu>)
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Dr. Lorenzo Paulatto
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