[CP2K-user] [CP2K:19566] Re: Significant discontinuity in EOS curver for FeO

[Krack Matthias]

Dear Kejiang

the default R_CUTOFF radius for the VDW_POTENTIAL is only 20 bohr (10.5 A) which can lead to a non-negligible noise in that energy contribution for a growing cell size, because the growth of the pair (neighbor) lists is not smooth (continuous). You can try a much larger R_CUTOFF radius, e.g. 25 A, for a smoother behavior.

I don’t think that a vdW correction is crucially needed for bulk FeO, but for FeO surfaces with H2/H2O adsorbed it makes sense most likely.

Best

Matthias

From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Kejiang Li <lyam_likej at 126.com>
Date: Thursday, 23 November 2023 at 23:16
To: cp2k <cp2k at googlegroups.com>
Subject: Re: [CP2K:19561] Re: Significant discontinuity in EOS curver for FeO
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
[cid:e91b0851-c9b8-4b72-ab97-f16fac2fda69]
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[https://groups.google.com/group/cp2k/attach/c32459892868/cell.jpg?part=0.1&view=1]

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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