[Wien] Magnetic material relaxation, RMT, MAE calculations

[Gerhard Fecher]

To find the magntic anisotropy is a "brute force" job (see chapter 4.6.4 of the textbook of J Kübler, Theory of itinerant electron magnetism),
that means you need really many k-points
(The question is what is "many" ? As answer from experience I would say: If you think you have enough then just take a lot more ! 
There is an example in Küblers book where Halilov used 372 248 k-points in the full Brillouinn zone.)
So how many k-points did you use ?

There is another thing one should keep in mind, some experimental  values may be influenced by the shape anisotropy
of the sample that was used (unfortunately in many experimental work not enough information is given).
MnAl has a rich binary phase diagramm, are you shure that the experimental values are for a single phase sample ?

What do you mean with experimental RMT ?
There is some older LEED theory where the muffin tin radii were calculated from the energy dependence of
low energy electron diffraction pattern. I guess that these have nothing to do with the RMT you set in Wien2k.


Ciao
Gerhard

====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
________________________________________
Von: wien-bounces at zeus.theochem.tuwien.ac.at [wien-bounces at zeus.theochem.tuwien.ac.at]" im Auftrag von "Jihoon Park [jpark61 at crimson.ua.edu]
Gesendet: Samstag, 4. Juni 2011 04:37
Bis: wien at zeus.theochem.tuwien.ac.at
Betreff: [Wien] Magnetic material relaxation, RMT, MAE calculations

Dear users,


I am really wondering if we have to "relax" structure everytime when calculating magnetic materials.
When relaxed, the magnetic properties, especially K value, become too far from experimental data; K value calculated from not relaxed structure is also far from the experimental one.

I tried force theorem as well, but that is still far from the experimental data too.

Everytime my calculated K value is reversed.
For example, energies for <001> and <100> are compared and used to calculate K.
But I do not understand why the energy for <100> is lower than that of <001>.
Experimentally, <001> is stable for MnAl.


And another qeustion is about RMT.
Is it okay to change RMT to fit experimental data?
I tried several times to fit experimental one, but still question myself if that is okay.