[Wien] Discrepancy in the simulation of the paramagnetic state

Mon Nov 28 13:42:28 CET 2016

There is some confusion here about types of paramagnetism.

If the spin-polarised and non-spin polarised results are the same, it merely means that the spin up and spin down bands are at equal energies.  Pt has no unpaired spins so no magnetic moment. It could from the calculation be diamagnetic or Pauli paramagnetic. As it is a metallic conductor, the latter is likely, so the non-magnetic form is the Pauli paramagnetic ground state. The spin up and spin down bands will acquire different energies if you apply a magnetic field.

The original query was concerned with Gd which has unpaired f electron spins and it is this type of system that becomes paramagnetic as you raise the temperature.

NiS which was also mentioned I assume contains Ni 2+ ions. In square planar environments these have no unpaired spins and so no magnetic moment and the compounds will be diamagnetic. In tetrahedral environments the ion has unpaired spins and so a magnetic moment. The change to no magnetic moment coincided with a first iorder phase transition so it is most likely linked to a change in  structure and hence the local environment of Ni.

Elaine A. Moore

The Open University, UK

________________________________
From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of Fecher, Gerhard <fecher at uni-mainz.de>
Sent: 28 November 2016 07:33
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] Discrepancy in the simulation of the paramagnetic state

I hope you agree that Pt is paramagnetic
I did two calculations for Pt, one was  spin polarized the other not.
The results are identical, no resulting magnetic moment (indeed, I started with one in the spin polarized case), did I play a trick or did Wien2k play a trick ?
but may be Wien2k can not be used to calculate the electronic structure of Pt, because it is paramagnetic (Pt, not Wien2k !).

I hope you agree that Pt is paramagnetic even at Zero temperature.
why do I need to include temperature effects to calculate the ground state of Pt (at 0 K, where else) ?
... and what should MtC calculations tell me about it ?

Remark 1:
Calculations may be  "spin polarized" (LSDA) or not (LDA) or they may be even more sophisticated "non-colinear spin polarized" or they may be for "disordred local moments"
or for "spin spirals", or ???,  just to name some.

Remark 2:
Materials may be diamagnetic, paramagnetic (Langevin, Pauli, van Vleck), ferromagnetic (localised moments, itinerant), ferrimagnetic (collinear, non-collinear), etc..

Therefore, I repeat my question:   How do you distinguish diamagnetic, paramagnetic, ferromagnetic, and ... states ?

The answer is for you, not for me.

I tried to calculate for Pt using Hohenberg Kohn DFT, but I could not find the functional, all I found was some approximation using wave functions.
Don't worry I will not ask a question about it ;-)

Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."

====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
and
Max Planck Institute for Chemical Physics of Solids
01187 Dresden
________________________________________
Von: Wien [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Xavier Rocquefelte [xavier.rocquefelte at univ-rennes1.fr]
Gesendet: Sonntag, 27. November 2016 12:46
An: wien at zeus.theochem.tuwien.ac.at
Betreff: Re: [Wien] Discrepancy in the simulation of the paramagnetic state

Just to add one more point to this funny discussion, the term
"paramagnetic" is sometimes used in the DFT litterature in an improper way.

It could clearly lead to misunderstanding for researchers who do not
know so much on how magnetic properties could evolve with temperature
and applied magnetic field. When you see in a paper "paramagnetic state"
simulated using DFT ... it is NOT paramagnetic at all, it is simply a
trick which must be considered with care as previously mentionned by
Peter, Eliane and Martin.

If you want to simulate a paramagnetic state you need to include the
temperature effects, i.e. you should consider the spin dynamics and the
competition between magnetic exchange interactions and thermal
fluctuations. This could be done, at least, using Monte-Carlo
calculations based on an effective hamiltonian constructed on top of DFT
parameters (including magnetic exchange and anisotropy at least).

Best Regards

Xavier

Le 27/11/2016 à 10:01, Fecher, Gerhard a écrit :
> How do you distinguish a diamagnetic, a paramagnetic, a ferromagnetic, and an antiferromagnetic state.
>
> Think !
>
> This will answer your question, hopefully.
>
> Ciao
> Gerhard
>
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
> "I think the problem, to be quite honest with you,
> is that you have never actually known what the question is."
>
> ====================================
> Dr. Gerhard H. Fecher
> Institut of Inorganic and Analytical Chemistry
> Johannes Gutenberg - University
> 55099 Mainz
> and
> Max Planck Institute for Chemical Physics of Solids
> 01187 Dresden
> ________________________________________
> Von: Wien [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Abderrahmane Reggad [jazairdz at gmail.com]
> Gesendet: Samstag, 26. November 2016 22:30
> An: wien at zeus.theochem.tuwien.ac.at
> Betreff: Re: [Wien] Discrepancy in the simulation of the paramagnetic state
>
> Thank you Prof Blaha for your quick answer.
>
> The Ni atom is 3d transition metal . But my question is about the simulation of the paramagnetic state. There are many people that considere that the paramagnetic state is the non-spin polarierd one and the magnetic moment is zero, but you say no and the magnetic moments exist in arbitrary directions and my quoting is about that.
>
> I have given 2 examples for that discrepancy with your statement.
>
> Best regards
> --
> Mr: A.Reggad
> Laboratoire de Génie Physique
> Université Ibn Khaldoun - Tiaret
> Algerie
>
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
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