[CP2K-user] [CP2K:19545] Re: Significant discontinuity in EOS curver for FeO

[Kejiang Li]

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
>>
>>  
>>
>>  
>>
>> [image: 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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