# [CP2K-user] [CP2K:13603] Magnetic Fe

Krack Matthias (PSI) matthi... at psi.ch
Tue Jul 7 07:53:52 UTC 2020

```Hi Andrew

Set the keyword MULTIPLICITY<https://manual.cp2k.org/cp2k-6_1-branch/CP2K_INPUT/FORCE_EVAL/DFT.html#MULTIPLICITY> to the appropriate value, i.e. the desired difference between alpha and beta electrons plus one. Moreover, you can specify the initial electronic configuration for each atomic kind using the BS section<https://manual.cp2k.org/cp2k-6_1-branch/CP2K_INPUT/FORCE_EVAL/SUBSYS/KIND/BS.html>.

HTH

Matthias

From: cp... at googlegroups.com <cp... at googlegroups.com> On Behalf Of Andrew Horsfield
Sent: Montag, 6. Juli 2020 16:01
Subject: [CP2K:13603] Magnetic Fe

I am attempting to carry out a calculation for ferromagnetic bcc Fe using CP2K 6.1. Attached are the input and output files.

The calculation runs to completion, but I am confused by the output. The multiplicity is not 1

Orbital energies  State     Spin  L     Occupation   Energy[a.u.]    Energy[eV]

1    alpha  0          1.000      -3.533760    -96.158487
2    alpha  0          1.000      -0.171394     -4.663878
1     beta  0          1.000      -3.422092    -93.119858
2     beta  0          1.000      -0.151638     -4.126285

1    alpha  1          3.000      -2.201116    -59.895424
1     beta  1          3.000      -2.092954    -56.952177

1    alpha  2          4.250      -0.282066     -7.675405
1     beta  2          1.750      -0.191730     -5.217225
yet the system appears to have zero spin moment:

!-----------------------------------------------------------------------------!
Mulliken Population Analysis

#  Atom  Element  Kind  Atomic population (alpha,beta) Net charge  Spin moment
1     Fe       1         8.000000     8.000000     0.000000     0.000000
2     Fe       1         8.000000     8.000000     0.000000    -0.000000
# Total charge and spin       16.000000    16.000000     0.000000    -0.000000

!-----------------------------------------------------------------------------!

Between these blocks of output seems to be a rescaling step which might explain the discrepancy:

Spin 1
Re-scaling the density matrix to get the right number of electrons for spin 1
# Electrons              Trace(P)               Scaling factor
16                18.500                        0.865

Spin 2
Re-scaling the density matrix to get the right number of electrons for spin 2
# Electrons              Trace(P)               Scaling factor
16                13.500                        1.185
Can anyone explain what is happening here and how I allow the system to be magnetic? Is there a keyword I need to add?

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