[Wien] Discrepancy in the simulation of the paramagnetic state
pieper
pieper at ifp.tuwien.ac.at
Tue Nov 29 11:33:48 CET 2016
My (and probably Xavier's) concern with Regaard's question was something
else.
I have no problem whatsoever with you finding an approximation for Pt
using wave functions. After all, your ground state model has zero static
local moments, as has the Pt you want to model. ;-)
However, the approximation seems at least dubious if the ground state
model and the low temperature state of the material differ. If the
material enters some magnetic state and the spin-polarized(!) DFT model
does not one might look for a problem with the structure data, some
structural phase transition, ...
So I am with Xavier, and I would at least advise to be careful with the
idea I understood Regaad did somehow get: Artificially compensate spins
(e.g. via LDA instead of LSDA) to find an approximation for the
paramagnetic phase at elevated temperature of a low temperature magnet.
There is at least one difference between the material and the model: the
model will NOT be paramagnetic (obtain a positive magnetization in an
applied magnetic field). Wether or not this (or any other differences
induced by the forced spin compensation) poses a problem will depend on
what situation one wants to model.
---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564
Am 28.11.2016 08:33, schrieb Fecher, Gerhard:
> 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
>>
>>
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>
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