[Wien] Spin units

[Peter Blaha]

Well, the definition of magnetic moments is not unique and often 
magnetic moments and magnetization are mixed and in particular chemistry 
and physics often use different conventions.

There is something which WE would call "effective magnetic moment", 
defined from the total angular momentum (or a single s electron produces 
a moment of 1.72 mu_B).

On the other hand, there is the magnetic moment of a single electron 
defined as   m = g mu_B S / h     and g is 2. This gives 1 uB/electron 
(spin-only value) and is used in solid state theory.
(Everybody would quote the (spin) magnetic moment of Fe as 2.2 mu_B, 
which comes from 2.2 unpaired electrons/cell).

Note, that without spin-orbit coupling, the orbital moment is always 
zero (you can calculate it in spin-polarized spin-orbit (lapwso) 
calculations).

Thus your 4 mu_B means 4 unpaired electrons.


Am 31.05.2024 um 16:37 schrieb Straus, Daniel B:
> Hello,
> 
> What are the units used for magnetic moment in the output? I can’t find 
> this in the usersguide or in old emails to this list, other than this 
> message 
> https://wien.zeus.theochem.tuwien.ac.narkive.com/zOaBf0py/reg-fixed-spin-moment-calculations <https://wien.zeus.theochem.tuwien.ac.narkive.com/zOaBf0py/reg-fixed-spin-moment-calculations> that implies the units are Bohr magneton, which I don’t think is correct based on my calculations. I am using ver 23.2.
> 
> For example, one of my converged SCF calculations (no spin-orbit 
> coupling, in case it’s relevant) says the following: “:MMTOT:  SPIN 
> MAGNETIC MOMENT IN CELL     =    4.00012”. What are the units for 
> 4.00012? Does this indicate that there are 4 unpaired spin-up electrons 
> per unit cell? This is for a system with four Cu^2+ per unit cell, so my 
> impression is that +1 SPIN MAGNETIC MOMENT = 1 spin up electron. I want 
> to confirm, though, because S=1/2 for Cu^2+ , so if this quantity is 
> defined such that each electron contributes +/- 1/2 to the moment, then 
> I have too many unpaired electrons in my system and something is wrong 
> with my input. I do not think this is in Bohr magnetons because I can’t 
> see why I would end up with an integer answer when the spin-only moment 
> of Cu^2+ is 1.73 Bohr magnetons.
> 
> Sincerely,
> 
> Daniel
> 
> P. S. Sorry for sending so many emails to this list.
> 
> Daniel Straus
> 
> Assistant Professor
> 
> Department of Chemistry
> 
> Tulane University
> 
> 5088 Percival Stern Hall
> 
> 6400 Freret Street
> 
> New Orleans, LA 70118
> 
> (504) 862-3585
> 
> http://straus.tulane.edu/ <http://straus.tulane.edu/>
> 
> 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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