[Wien] About the magnetic moment of vanadium in vanadium sulphide

Thu Sep 7 13:31:02 CEST 2017

I agree, there is some confusion. There probably always is.

The confusion here is mainly about definition para-, dia-, ferro-, 
antiferro-, heli-, or non-  magnetic. This comes up every now and then.

As I said before, I like the following distinction.

a) Define Non-Magnetic ONLY in context of calculations, and there as a 
model where in the converged ground state all local moments are smaller 
than the numerical noise.

The rest were defined much earlier from an experimental point of view. 
They all are meant to distinguish response to external magnetic field - 
a field that DOES NOT EXIST in your off the shelf DFT!

b) Various kinds of dia- and para-magentism specify wether the 
magnetization induced by an applied field is opposite (diamagnetic) or 
parallel (paramagnetic) to the field.

c) Magnetically ordered states (FM, AFM of various types, ferri-, heli-, 
spin density wave-, ...) are PM in this sense. They are distinguished by 
the spacial arrangement of non-zero static magnetic moments (all 
parallel, exactly compensated antiparallel, not compensated 
antiparallel, not collinear, varying in size continuously, ...).

So in response to your points:

1.: Yes, but a PM response just might be due to some unnoticed AF 
ordered state. Because of Ockham's razor one would have to convince me 
of that, but who know's?

2.: Yes, you can get a non-magnetic ground state from a spin-resolved 
calculation. 'Local moments' always refers to the moments within RMT's 
(or whatever the DFT code supports to assign local moments). The 
electron spins are of course always there, but spin up and down can 
compensate - and often will compensate due to spin degenerate ground 
states.

3.: No, I would be very surprised (and suspicious) if the calculations 
yield some exactly compensating moment on S. For exact compensation, 
that is an AF arrangement, you have to have the same element pointing 
moments in opposite directions. Even the crystalografic lattice sites 
occupied by the antiparallel moments should be the same. I know of no 
counter example but would be interested if there is one. In VS Vanadium 
just might split one of its sublattices into such an AF arrangement.

4.: There is a DOS plotted in the work A. Reggad linked in his earlier 
question.

5.: That DOS certainely looks metalic and the authors claim agreement 
with experiment.

Best regards,

Martin Pieper

---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564

Am 07.09.2017 11:02, schrieb E.A.Moore:
> I have been following this thread and I think there is some confusion.
> 
> 1. On the thread it said that the experiment showed it was Pauli
> paramagnetic. This is the type of magnetism displayed by some metals
> e.g. sodium which is only apparent if you apply a magnetic field.
> 
> 2. If you include spin in your calculation (GGA or GGA + U) you can
> only get ferromagnetic, antiferromagnetic or ferromagnetic states. (An
> earlier thread deals with how to get paramagnetic states). I think you
> can only get a nonmagnetic state if you do not include spin? A
> material with Pauli paramagnetism will be antiferromagnetic in
> straight forward spin-including calculations.
> 
> 3. I assume the 0.05 muB refers to the magnetic moment on V. If
> vanadium sulphide is antiferromagnetic and the magnetic moment on
> Vanadium is 0.05 muB, then there must be a balancing magnetic moment
> on the sulphur.
> 
> 4. I suspect this compound might be alloy-like. Is there considerable
> mixing of V and S in the valence bands?
> 
> 5. Assuming your formula is VS, it might be worth noting that VO shows
> some metallic physical properties.
> 
> Elaine A. Moore
> Reader in theoretical chemistry
> The Open University
> 
> 
> 
> -----Original Message-----
> From: Wien [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf
> Of Fecher, Gerhard
> Sent: 07 September 2017 08:12
> To: A Mailing list for WIEN2k users
> Subject: Re: [Wien] About the magnetic moment of vanadium in vanadium 
> sulphide
> 
> 0.05 muB does not mean that it is antiferromagnetic ! what was your
> charge convergence criterion ?
> 
> You did never answer my question whether you started the EECE
> calculation from a converged GGA calculation.
> 
> Why do you like to have an afm state when the experiment tells it is 
> not ?
> 
> 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: Donnerstag, 7. September 2017 00:26
> An: wien at zeus.theochem.tuwien.ac.at
> Betreff: Re: [Wien] About the magnetic moment of vanadium in vanadium 
> sulphide
> 
> Hi Martin
> 
> The problem is that I want to know if it's possible to get a such
> value of 0.05 MB for atomic magnetic moment for the AFM state of
> vanadium sulphide in NiAs structure.
> 
> Hafner and Hobbs have found all the calculations converged to the non
> magnetic state because they have used the GGA method. To get the AFM
> state they have to use either the EECE or GGA+U methods.
> 
> I hope you touch the problem
> 
> 
> Best regards
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