[Wien] How to know if the M+2 has a high spin from calculation?

Abderrahmane Reggad Sat, 26 Aug 2017 04:21:02 -0700

Dear wien2k users

We know that the ion Fe+2 has a high spin configuration (3d6 (teg(4) eg(2))
because the crystal field effect..

How to check that from calculation ?

Best regards

Answer of Pr Blaha

Re: [Wien] How to know if the M+2 has a high spin from calculation?

Peter Blaha Mon, 28 Aug 2017 09:16:39 -0700

It is not always so simple to find the charge state of an atom. It really depends on the material you are looking at.

But for Fe 2+ or 3+ in high-spin configuration of some Fe-oxide it is rather simple:

Fe3+ in high-spin conf. has 3d5-up and no 3d-dn electrons. This makes a spin-moment of 5 per Fe atom (if you have a ferromagnet, you may see :MMTOT a multiple of 5, but if it is a ferri or antiferromagnet MMTOT may be zero or different). The MMIxxx value of this atom will be large (around 4).

If it is Fe 2+, we have 3d5-up/3d1-dn; i.e. only a moment of 4.
The MMIxxx of Fe 2+ is usually around 3.6 muB.

Total charges within an atomic sphere are usually not suitable to decide on that.

An alternative is Bades AIM theory and the AIM program can calculate these Bader charges. However, also for these Bades charges, the differences between Fe 2+ or 3+ might be samll (maybe 0.1 e at most).

So the spin-analysis is best, if you have a high-spin state. Low spin-states and/or different symmetries (tetrahedral vs. octahedral,...) have different laws and you need some knowledge of crystal field theory to get an idea what can happen.

Reference; https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg16285.html