[QE-users] QE-7.1 and DFT+U

[Iurii TIMROV]

Dear Mahmoud,


> https://arxiv.org/abs/2108.12758


Thank you for this reference! I am going to read it.


> You argue that since O atom is not magnetic, the starting_magnetization for that atom is taken to be zero.


I was not precise enough. I meant for FeO, while in general this might not be the case (I don't have much experience with this though).


In the older versions of QE the starting_magnetization for O was 0.0. And the calculations were converging to the solution where the magnetic moments on O are zero. That's why I removed starting_magnetization for O in the new example which means that the default value of 0.0 is used for O. I tried to specify the finite value of starting_magnetization for O in FeO but still the calculation convergences to the solution where the magnetic moments on O are zero.


> By "hard-coded" I do not understand what you mean.


I mean that it is implemented in the routine PW/src/tabd.f90 in the older version of QE and that it was not possible to change these parameters from the input file. In contrast, in QE7.1 the starting atomic occupations of Hubbard atoms can be controlled from the input (but by default they are read from the pseudopotentials).


Greetings,

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: Mahmoud Payami Shabestari <mpayami at aeoi.org.ir>
Sent: Wednesday, June 29, 2022 3:38:54 PM
To: Iurii TIMROV; Quantum ESPRESSO users Forum
Subject: Re: [QE-users] QE-7.1 and DFT+U

Dear Iurii,


You argue that since O atom is not magnetic, the starting_magnetization for that atom is taken to be zero.
I would like to attract your attention to the work:

https://arxiv.org/abs/2108.12758

in which it is shown that the GS of UO2 is obtained for non-zero starting_magnetization of O-atom.
I have to check the results from QE-7.1 of my inputs (of course in new syntax) of the above work to see if I get the same results. Otherwise, the occupations were wrongly dependent on the starting_magnetization of O-atoms, and now it is bug-fixed. By "hard-coded" I do not understand what you mean.
Thank you again.

Best regards,
Mahmoud





From: Iurii TIMROV via users <users at lists.quantum-espresso.org>
To: Mahmoud Payami Shabestari <mpayami at aeoi.org.ir>, "Quantum ESPRESSO users Forum" <users at lists.quantum-espresso.org>
Date: Wed, 29 Jun 2022 11:44:03 +0000
Subject: Re: [QE-users] QE-7.1 and DFT+U

Dear Mahmoud,

> Explicitly, the starting_magnetization for O is removed in the new one. Does it mean the default value is still zero or the code searches for a better starting magnetization?

O atoms are nonmagnetic so that's why starting_magnetization for O was removed.

> But, comparing the results from qe-7.1 and qe-6.7, one notices significant changes in the input and outputs of feo_user_ns files.

FeO is metallic in DFT while it is insulting in nature. The difference between the new and old behaviour of QE is the starting occupations of the Fe-3d manifold. In older versions of QE (before 7.1) the starting occupations are hard-coded to be 6 (see PW/src/tabd.f90) while in QE7.1 the starting occupations are read from the pseudopotential (in this particular example it is 7). It turns out that in this example different starting occupations for Fe-3d states lead to the convergence to different metallic ground states of FeO, but in any case both are wrong ground states (one needs +U and to use starting_ns_eignevalue to open a gap and thus obtain the correct ground state). But if you want to restore the old behaviour of QE in the new version (i.e. 7.1) you need to specify in the input the new keyword Hubbard_occ(1,1) = 6.0 and Hubbard_occ(2,1) = 6.0 (because you have Fe1 and Fe2) - in this case the code reads the starting occupations from the input and not from the pseudopotential.

Greetings,
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> on behalf of Mahmoud Payami Shabestari via users <users at lists.quantum-espresso.org>
Sent: Wednesday, June 29, 2022 1:16:53 PM
To: users at lists.quantum-espresso.org
Subject: [QE-users] QE-7.1 and DFT+U

Dear QE developers,

Hi.
In the new release QE-7.1, I investigated through the example08 of PW, the example of FeO.
In the release-notes, Incompatible changes, line 3, it is mentioned that "input syntax" is changed.
But, comparing the results from qe-7.1 and qe-6.7, one notices significant changes in the input and outputs of feo_user_ns files.
Explicitly, the starting_magnetization for O is removed in the new one. Does it mean the default value is still zero or the code searches for a better starting magnetization?
Any comments is highly appreciated.

With best regards,
Mahmoud Payami
NSTRI, AEOI, Tehran, Iran

Email: mpayami at aeoi.org.ir
Phone: +98 (0)21 82066504


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