How to set ISPIN for magnetic materials above their critical temperature?

Queries about input and output files, running specific calculations, etc.


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wdv
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How to set ISPIN for magnetic materials above their critical temperature?

#1 Post by wdv » Mon Sep 06, 2010 8:06 am

Dear all,

For nonmagnetic systems like Al and Si, we set ISPIN=1. For FM and AFM systems below their critical temperatures like Fe and NiO, we set ISPIN=2. But for Fe and NiO ABOVE their critical temperatures, how to set ISPIN? 1 or 2?

Thank you very much!
Last edited by wdv on Mon Sep 06, 2010 8:06 am, edited 1 time in total.

boris
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How to set ISPIN for magnetic materials above their critical temperature?

#2 Post by boris » Mon Sep 06, 2010 10:30 am

Hi

In my opinion, ISPIN doesn't have anything to do with being below or above the critical temperature. As soon as the system you are considering is magnetic, you need to set ISPIN=2.

Then, you need to set the correct magnetic moments (using the MAGMOM tag) in order to reproduce the magnetic ordering.

What you're trying to say, I presume, is that above the critical temperature, systems can be paramagnetic. For paramagnetism, I think the best choice is to set ISPIN=1, for DFT calculations. For DFT+U or hybrid calculations, where electrons are localized, then I think it is impossible to model paramagnetism. But I may be wrong.

Regards.

<span class='smallblacktext'>[ Edited Mon Sep 06 2010, 12:33PM ]</span>
Last edited by boris on Mon Sep 06, 2010 10:30 am, edited 1 time in total.

forsdan
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How to set ISPIN for magnetic materials above their critical temperature?

#3 Post by forsdan » Mon Sep 06, 2010 11:26 am

There is always issues to model phases at high finite temperatures from T = 0 K calculations. If you truly want to model the paramagnetic phase I would say that neither ISPIN = 1 nor ISPIN = 2 is an approriate choice. To use the nonmagnetic solution as an approximation for the paramagnetic state should definitely be questioned before usage, since its validity and accuracy for the bulk properties of the paramagnetic phase will depend on the specific system. I would rather look through the literature and consider approaches such as the Disorder Local Moment model or alternatives.

Cheers,
/Dan

<span class='smallblacktext'>[ Edited Mon Sep 06 2010, 01:30PM ]</span>
Last edited by forsdan on Mon Sep 06, 2010 11:26 am, edited 1 time in total.

boris
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How to set ISPIN for magnetic materials above their critical temperature?

#4 Post by boris » Mon Sep 06, 2010 2:01 pm

I agree with Dan. ISPIN=1 remains definitely questionable for the modelling of paramagnetic phases.
Last edited by boris on Mon Sep 06, 2010 2:01 pm, edited 1 time in total.

wdv
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How to set ISPIN for magnetic materials above their critical temperature?

#5 Post by wdv » Tue Sep 07, 2010 12:00 pm

Thank you, boris and Dan.
Last edited by wdv on Tue Sep 07, 2010 12:00 pm, edited 1 time in total.

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