[CP2K-user] [CP2K:19561] Re: Significant discontinuity in EOS curver for FeO

[Kejiang Li]

Dear Matthias, 

I really appreciate your patience in responding to my question point by 
point.

I researched the literature and saw no published EOS results for FeO using 
cp2k. 

I finally found that it was the VDW_POTENTIAL that led to the significant 
discontinuity in my EOS curve. After eliminating the VDW_POTENTIAL 
potential in all my test codes, CP2K provides a continuous EOS curve that 
is quite normal.  Please see the attached figure.

I never expected that VDW_POTENTIAL might have such an apparent lousy 
effect on the FeO structure. What do you think might be the possible 
fundamental mechanism for this issue? As I want to simulate the reaction 
between FeO surface and H2/H2O in the future, I think it might be necessary 
to include VDW_POTENTIAL.

Could you please provide your opinion regarding whether 
including VDW_POTENTIAL in my future calculations is necessary?

Thanks a lot.

Best,
Kejiang
[image: vdw2.png]
On Thursday, November 23, 2023 at 11:41:34 PM UTC+8 Krack Matthias wrote:

Dear Kejiang

   - 1. You didn't set the VDW_POTENTIAL. Don't we need to 
   consider VDW_POTENTIAL for FeO?

Not sure if that is needed for bulk FeO. Did you check the work of other 
authors? Did they apply such a vdW correction for bulk FeO?

   - 2. You didn't set the initial value for MAGNETIZATION. Is this also 
   not necessary for FeO?

The &BS section does the same, i.e. sets the initial on-site electronic 
configuration for the iron atoms, and it allows for a more detailed control.

   - 3. You didn't set the UKS and MULTIPLICITY. Is the default setting for 
   UKS and MULTIPLICITY enough for FeO?

Yes, it is for AFM FeO as I already explained.

Matthias

On Thursday, November 23, 2023 at 5:39:55 PM UTC+8 Krack Matthias wrote:

Dear Kejiang

 

I have added a howto page <https://www.cp2k.org/howto:dft_u> to the CP2K 
wiki for DFT+U calculations with an EOS calculation for cubic FeO as an 
example.

 

HTH

 

Matthias

 

*From: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
Kejiang Li <lyam_... at 126.com>
*Date: *Wednesday, 22 November 2023 at 07:19
*To: *cp2k <cp... at googlegroups.com>
*Subject: *[CP2K:19547] Re: Significant discontinuity in EOS curver for FeO

Dear all, 

Here, I also attached the test results with different sizes of supercells. 
There is still a sharp decrease or discontinuity on the left side of the 
lowest point.

Could anyone provide any guidance?

Thanks a lot.

Best regards,

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

*Error! Filename not specified.*

*Error! Filename not specified.**Error! Filename not specified.*

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