[Wien] Help on AFM Structure

Rocquefelte xavier.rocquefelte at cnrs-imn.fr
Mon Jan 20 07:01:40 CET 2014 

Your question is not anymore a WIEN-list issue.
Indeed, it corresponds to the way to investigate magnetic properties.
Many strategies exist. One strategy, for instance, consist in estimating 
the magnetic interactions (J values) bases on a mapping analysis.
Such mapping analysis requires to consider many magnetic orders (FM and 
AFM).

In your case, what should you do? It is a matter of research direction 
and I feel that this is not the purpose of the wien-list to define your 
own project.
 From the userguide and all the available documents on the WIEN2k 
website, you can now generate different magnetic structures.
Do it... and compare them in terms of total energy. Are you expecting 
that the wien-list will generate the inst files for you?
It is definitely not the best way to learn.

One remaining question could be the following: which magnetic order 
should you generate?
There are two main approaches:

- a mathematical one ... you generate all possible combinations ... i.e. 
a lot ... and you will find the more stable one
- a chemist one ... look at the atomic structure ... what will be the 
largest super-exchange from the Kanamori-Goodenough rules?

Finally, don't forget that you will need a good k-mesh and a good 
accuracy to have a proper energy comparison between all the models.

Cheers

Xavier






Le 1/19/2014 8:00 PM, Chinedu Ekuma a écrit :
> Hi Rocqueflte,
> The experimental magnetic structure is not known. What I wanted to do 
> is to study it in terms of the various AFM structures. However, as I 
> explained before, constructing the various AFM orders is confusing. 
> For example, the Collinear AF, Bicollinear AF, Neel AF, A-type, etc. 
> If you can explain to me how I can achieve this using the structure I 
> attached before, it will be appreciated.
>
> From your earlier response, "Do I repeat the up and down spins for all 
> the Fe to get the CAF?
>
> Once again, thanks for your assistance so far.
>
> *C.  Ekuma*
> /
> /
> ////
>
>
> On Sunday, January 19, 2014 11:23 AM, Rocquefelte 
> <xavier.rocquefelte at cnrs-imn.fr> wrote:
> If you know the experimental magnetic structure, then you must specify 
> the spin state of each iron atoms in accordance.
> If you don't know the experimental ground state magnetic structure, 
> you will need to try a series of magnetic orderings.
> In the second case, it must be done with care (same cell and space 
> group) because the energy differences between two magnetic states can 
> be quite small (few meV).
>
> Cheers
>
> Xavier
>
>
> Le 1/19/2014 2:25 PM, Chinedu Ekuma a écrit :
>> Hi Rocqueflte,
>> Thank you very much for your explanations. Do I repeat it all through 
>> in pairs as you showed or just for the Fe1 and Fe2?. My concerns was 
>> that due to the structure, I couldn't identify a plane for the AFM. 
>> Assuming up is u and down is d, do I just do: ududududud... for the 
>> whole Fe in the structure? If this is the case, how then do one 
>> differentiate this from other AFM configurations like A-type or 
>> bicollinear?
>>
>> Once again, thank you for your time and explanations.
>>
>> *C.  Ekuma*
>>
>> ////
>>
>>
>> On Sunday, January 19, 2014 2:07 AM, Rocquefelte 
>> <xavier.rocquefelte at cnrs-imn.fr> 
>> <mailto:xavier.rocquefelte at cnrs-imn.fr> wrote:
>> Here is one way to do it.
>> Keep the P1 symmetry (if really needed for the AFM collinear magnetic 
>> order you need).
>> Generate the file case.inst (input file of lstart created after 
>> symmetry).
>> Here I provide the beginning of this file. You can see the electronic 
>> configuration of Fe1 and Fe2.
>> Imagine that in your collinear magnetic phase Fe1 and Fe2 are 
>> respectively up and down.
>> Thus you must change the case.inst file in the following manner.
>>
>> Fe
>> Ar 3
>> 3, 2,2.0  N
>> 3, 2,2.0  N
>> *3,-3,2.5  N**
>> **3,-3,0.0  N*
>> 4,-1,1.0  N
>> 4,-1,0.5  N
>> Fe
>> Ar 3
>> 3, 2,2.0  N
>> 3, 2,2.0  N
>> *3,-3,0.0  N**
>> **3,-3,2.5  N*
>> 4,-1,1.0  N
>> 4,-1,0.5  N
>>
>> For Ga atoms, if they are non-magnetic (or not far) the best is to 
>> start with a non-magnetic atomic configuration as below:
>>
>> Ga
>> Ar 4
>> 3, 2,2.0  N
>> 3, 2,2.0  N
>> 3,-3,3.0  N
>> 3,-3,3.0  N
>> 4,-1,1.0  N
>> 4,-1,1.0  N
>> *4, 1,0.5  N**
>> **4, 1,0.5  N*
>>
>> Then you must run "x lstart", and continue initialization "x dstart 
>> -up / x dstart -dn" ... It will generate the proper collinear 
>> magnetic order ...
>> At this stage you don't need to use the option "run_afm" ... this 
>> option is needed only if you cannot keep the magnetic order you have 
>> previously defined.
>>
>> More details are available in the userguide and here:
>>
>> http://www.wien2k.at/reg_user/faq/afm.html
>>
>> www.wien2k.at/reg_user/textbooks/WIEN2k_lecture-notes_2013/magnetism.pdf 
>> <http://www.wien2k.at/reg_user/textbooks/WIEN2k_lecture-notes_2013/magnetism.pdf>
>>
>> http://www.wien2k.at/reg_user/textbooks/WIEN2k_lecture-notes_2013/Relativity-NCM.pdf
>>
>> Best Regards
>>
>> Xavier
>>
>>
>>
>>
>>
>>
>> Le 1/19/2014 1:41 AM, Chinedu Ekuma a écrit :
>>> Dear All,
>>> I am trying to construct a collinear AFM structure from the attached 
>>> file. Please, any help will be greatly appreciated.
>>>
>>>  Thanks.
>>> *C.  Ekuma*
>>>
>>>
>>>
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>>
>>
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