[CP2K-user] [CP2K:19551] Re: Significant discontinuity in EOS curver for FeO

[Krack Matthias]

Dear Kejiang

You cite a sentence describing the on-site multiplicities for each iron atom. Within an antiferromagnetic setup, e.g. for cubic FeO, the overall MULTIPLICITY of the simulation cell is 1 (the default value in CP2K with LSD).

I would not trust the answer of ChatGPT concerning the multiplicity of Fe(+2) and Fe(+3). I suggest to have a look at a text book.

Matthias

From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Kejiang Li <lyam_likej at 126.com>
Date: Wednesday, 22 November 2023 at 05:02
To: cp2k <cp2k at googlegroups.com>
Subject: Re: [CP2K:19545] Re: Significant discontinuity in EOS curver for FeO
Dear Mathias,

I have read the excellent paper you provided, in which it states: "The simulations were performed with a multiplicity (2S + 1)Fe2+ = 5 for systems with a ferrous iron and (2S + 1)Fe3+ = 6 for systems with a ferric iron, respectively."

Should I set the MULTIPLICITY in cp2k to 5 for FeO system? Does MULTIPLICITY have a noticeable influence on the EOS curve?

Btw, could you please help to explain how to calucalte the MULTIPLICITY for Fe2+ or Fe3+? I got the following results from ChatGPT, which differs from yours.



1.    Fe²⁺ (Iron(II) Ion): Loses two electrons.
·         Electron configuration: [Ar]3d6
·         There are 6 electrons in the 3d orbital. According to Hund's rule, the maximum multiplicity arises when the electrons are unpaired as much as possible. The 3d orbital can hold up to 10 electrons, so with 6 electrons, 4 of them can be paired, and 2 are unpaired.
·         Total spin S is the number of unpaired electrons divided by 2, which is 2/2=1.
·         Multiplicity = 2S+1=2×1+1=3.
·         Therefore, the multiplicity for Fe²⁺ is 3.

2.    Fe³⁺ (Iron(III) Ion): Loses three electrons.
·         Electron configuration: [Ar]3d5
·         There are 5 electrons in the 3d orbital. With 5 electrons, 3 can be unpaired while 2 are paired.
·         Total spin S is 3/2=1.5.
·         Multiplicity = 2S+1=2×1.5+1=4.
·         Therefore, the multiplicity for Fe³⁺ is 4.
Thanks a lot.

Best regards,
Kejiang
On Wednesday, November 22, 2023 at 8:58:45 AM UTC+8 Kejiang Li wrote:
Dear Matthias,

Thanks a lot for providing the information.

Could you please provide your input file for CP2K for reference? Maybe I made a mistake somewhere.

Best regards,
Kejiang
On Tuesday, November 21, 2023 at 11:29:14 PM UTC+8 Krack Matthias wrote:
Hi

The EOS curve for FeO (2x2x2) looks fine for me (see attached plot) using PBE and the suggested Hubbard U(eff) value of 1.9 eV for iron<https://pubs.acs.org/doi/10.1021/acs.est.7b01670> with CP2K.

Best

Matthias


[A graph of a function    Description automatically generated]

From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Jürg Hutter <hut... at chem.uzh.ch>
Date: Tuesday, 21 November 2023 at 09:46
To: cp... at googlegroups.com <cp... at googlegroups.com>
Subject: Re: [CP2K:19537] Re: Significant discontinuity in EOS curver for FeO
Hi

what is the setup for the QE calculation (cell, k-points, magnetization)?

regards
JH

________________________________________
From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Kejiang Li <lyam_... at 126.com>
Sent: Monday, November 20, 2023 2:26 AM
To: cp2k
Subject: [CP2K:19531] Re: Significant discontinuity in EOS curver for FeO

Dear all,

To add one more point.
As it was said, using a reference cell might solve this problem (https://groups.google.com/g/cp2k/c/N52jLt2yAIQ/m/JAlV3KTVUtIJ). You will notice that I used &CELL_REF in my input script, which did not solve my problem.

Thanks.
Kejiang

On Monday, November 20, 2023 at 9:00:11 AM UTC+8 Kejiang Li wrote:
Dear CP2K community,

I am calculating the EOS for FeO with a 2*2*2 supercell. But there is always a significant discontinuity (sharp decrease) in the range of 4.3-4.4 angstrom lattice constant in the EOS curves, as shown in the figures below.

I have done the following tests:
- the convergence of the energy with different cutoffs;
- using different functionals, including PBE, HSE, and SCAN;
-including HSE with different HF fractions;
-using different magnetization and +U settings.
However, all the tests produce similar results with an apparent discontinuity (4.3-4.3 A) .

This discontinuity is not observed in the Quantum Espresso results conducted by myself and in the results of literature that generally used VASP.  I believe that the CP2K program might cause this problem.

Can you give me more suggestions on how to do further tests?

Here, I also attached one sample code I used during my tests.

Thanks a lot.

Best regards,
Kejiang
The University of Science and Technology Beijing

[cp2k_functionals.jpg]
[cp2k_mag_u.jpg][cp2k_mag_u2.jpg]

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