Spin polarised calculation for bulk iron (16 atoms)

[Unmesh Mondal]

Dear Cp2k Users,

I am new to cp2k and wish to do a spin polarised calculation of bulk Iron  (Fe : 16 atoms, gamma point). Switching on UKS (spin unrestricted Kohn Sham) ensures the spin polarised part  and the MULTIPLICITY " " ensures the initial spin state of the whole system. I have used smearing and I expect the magnetic moment on each atom to be around 2.28 (using quantum espresso).

1) What value (and approach) of MULTIPLICITY should I use to get the global minima (state corresponding to the aforementioned magnetic state) ?

2) I have attached an input file. Please guide me if I have missed out or supplied any wrong input.

Unmesh Mondal
PhD student
IISER Pune
India     

[Tiziano Müller]

Hi Unmesh

Am 25.04.2018 um 12:18 schrieb Unmesh Mondal:
> I am new to cp2k and wish to do a spin polarised calculation of bulk
> Iron  (Fe : 16 atoms, gamma point). Switching on UKS (spin unrestricted
> Kohn Sham) ensures the spin polarised part  and the MULTIPLICITY " "
> ensures the initial spin state of the whole system.

Are you sure? Check your output right below "Guess for atomic kind: Fe".
This should tell you the used initial spin state.

With CP2K 5.1 and later you can use the MAGNETIZATION keyword for the
KIND section (with a value of 2.3 for iron) to get a proper initial
state, see

https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/SUBSYS/KIND.html

If you are using an older version (<5.1) use the Broken Symmetry section
instead to achieve the same thing:

https://manual.cp2k.org/cp2k-4_1-branch/CP2K_INPUT/FORCE_EVAL/SUBSYS/KIND/BS.html

Best regards,
Tiziano

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Tiziano Müller
University of Zurich
Department of Chemistry
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CH-8057 Zürich

Tel: +41 44 63 54234
www.chem.uzh.ch
tiziano...@chem.uzh.ch

[Daniele Ongari]

Hi Tiziano, 
I'm interested in this topic because I have problem to make materials (MOFs) with Fe converge and I want to start to the bulk Fe as a test case.

I wonder how your suggestion is supposed to work (I'm using CP2K-5.1 too).
1) Without specifying the system MULTIPLICITY this is by default 0 (which is treated as 1 in CP2K) that means that no broken symmetry is occurring: spin1 and spin2 will be rescaled and basically the effect of specifying the MAGNETIZATION is null
2) If considering that the system has 16 Fe atoms, one used 1+16*2.3= 37.8 as MULTIPLICITY (assuming ferromagnetic configuration), CP2K aborts with the error "An integer type object was expected".

So, how can someone specify a MAGNETIZATION that doesn't sum up into an integer total magnetization?

The problem I see is another, that I'm not able to make the calculation converge with MAGNETIZATION 2 and MULTIPICITY 1+16*2=33 (so no problems with non-integer numbers), but this is a problem to solve in the &MIXING section, right?
Do you have any working settings for make the bulk Fe converge? I think you managed to do so for the Delta-test of Stefaan Cottenier.

Thank you very much for your help

Daniele

[Ari Paavo Seitsonen]

Dear Daniele,

  My few thoughts,

  What you could use instead of "MULTIPLICITY" is the keyword "FIXED_MAGNETIC_MOMENT", https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/SCF/SMEAR.html#list_FIXED_MAGNETIC_MOMENT , if you indeed try to force a magnetic moment. Usually this is, however, not done but the system is let to relax its electronic structure and find the final magnetisation self-consistently. "MULTPLICITY" is meant for systems with well-defined electronic shells (open- or closed-shell), with a gap between the occupied and un-occupied states, whereas with the smearing one goes for different tools and keywords. The suggestion was to used the keyword "MAGNETIZATION" to get a reasonable initial guess and then let the system relax and find its magnetic moment; if you have convergence problems, you might try with "FIXED_MAGNETIC_MOMENT" in the first calculation, once that converges you read the previous density (densities, including the spin polarisation) and try without any constraint on the magnetisation.

    Good Luck from Half-Sunny Paris,

       apsi

Le mer. 28 août 2019 à 11:42, Daniele Ongari <daniele...@gmail.com> a écrit :

Hi Tiziano, 
I'm interested in this topic because I have problem to make materials (MOFs) with Fe converge and I want to start to the bulk Fe as a test case.

I wonder how is your suggestion supposed to work.

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