Could a fractional spin number be possible

Bader charge density analysis

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jianmin
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Joined: Fri Jan 15, 2010 2:39 am

Could a fractional spin number be possible

Post by jianmin » Wed Apr 10, 2019 12:43 am

Dear all and especially Prof. Graeme,

I was trying to calculate the spin charge density of the monomer of a homogeneous catalyst, the ball-and stick structure of which is as in the attachment. The atom in dark yellow and in the center is iron (Fe), linking to two ligands.

After a single-point energy calculation and issuing three commands:
chgsum.pl AECCAR0 AECCAR2
chgsplit.pl CHGCAR
bader CHGCAR_mag -ref CHGCAR_sum
I have got the spin numbers of all atoms of the system.

Oddly, the spin number for Fe atom is calculated to be 3.4991. Does it mean that the Fe atom has 3.5 unpaired electrons? Is it meaningful physically? Or is there anything wrong with my INCAR settings?
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graeme
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Re: Could a fractional spin number be possible

Post by graeme » Wed Apr 10, 2019 3:09 am

That seems ok to me.

jianmin
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Re: Could a fractional spin number be possible

Post by jianmin » Wed Apr 10, 2019 5:39 am

Prof. Graeme, Thanks.

Since it is okay to you, if it was you to report the spin number in a paper, what would you write ? 3.5 ? Isn't a spin number always an integer?

graeme
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Re: Could a fractional spin number be possible

Post by graeme » Wed Apr 10, 2019 12:15 pm

It's true that the total spin will be an integer, but the integrated spin around an atom does not need to be.

This is similar to the charge of an atom. We typically think about formal (integer) charges, but in reality electrons do not completely localize on atoms in the solid state.

jianmin
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Joined: Fri Jan 15, 2010 2:39 am

Re: Could a fractional spin number be possible

Post by jianmin » Fri Apr 12, 2019 7:44 am

Thanks Prof. Graeme ! Lesson learned.

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