[Wien] AFM structure for double perovskite oxide

[Gavin Abo]

If you look at the AFM Cr example of Exercise 7 on slide 17 of [1], the 
struct file has Cr1 atom with a multiplicity of 1 at a non-equivalent 
atomic position of (0,0,0) and it also has Cr2 atom with a multiplicity 
of 1 at an non-equivalent atomic position of (0.5, 0.5, 0.5).  Since 
multiplicity is 1, there are no equivalent atomic positions in this example.

At [2], you can see during the "instgen_lapw -ask" step during execution 
of "init_lapw" that "u" was entered for Cr1 and "d" was entered for 
Cr2.  After the scf calculation, the Cr1 moment from the calculation was 
1.13184 for MMI001 and the Cr2 moment was -1.13184 for MMI002.  The Cr1 
and Cr2 are antiferromagnetic [3] with their moments having equal 
magnitude and opposite sign resulting zero total moment (MMTOT).

Similar for your case, I think you need to ask and answer yourself the 
same questions as you would for the above example. In other words:  What 
are the non-equivalent atomic positions for Cr (but for Fe and Ni in 
your case)?  What is the multiplicity of each non-equivalent atomic 
position?  What are the equivalent atomic position for Cr (i.e, Fe and 
Ni in your case), if any? What atoms at the non-equivalent and 
equivalent [4] atomic positions give the AFM configuration(s) of 
interest and are expected to cancel to give a zero total moment?  Of 
note, if you not familiar with what the multiplicity is in the struct 
file, refer to section "4.3. THE CASE.STRUCT.FILE" on page 40 in the 
usersguide for WIEN2k 19.1 and 19.2 [5].

I realize the use of runafm_lapw in the above Cr example might be 
misleading as runsp_lapw typically has to be used in most cases as 
explained in previous posts in the mailing list archive such as [6-8].

Also, since the configuration set in case.inst with instgen_lapw is just 
the initial one that could change during the scf as explained in [9,10], 
don't forget to check the final magnetic order that comes out of the scf 
to see if you have AFM or not [11].

Though, in some cases when the scf does not result in the expected spin 
state, it might be possible to force a particular state as described in 
previous posts in the mailing list archive such as [12-14].

There used to be a presentation online that I think illustrated WIEN2k 
calculations on a structure for different AFM configurations like Type 
G, Type A, and Type C that might been of interest to you, but 
unfortunately I could not find it again in a Google search.  So 
something might have happened to the website that was hosting it.  It 
might have been the presentation "P. Blaha: “Magnetic and charge order 
phase transition in YBaFe2O5" seen in [15].

[1] http://susi.theochem.tuwien.ac.at/events/ws2015/Exercises_15.pdf
[2] 
http://wien2k-algerien1970.blogspot.com/2016/02/how-to-do-antiferromagnetic-calculation.html
[3] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg13159.html
[4] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg17879.html
[5] http://www.wien2k.at/reg_user/textbooks/usersguide.pdf
[6] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg16805.html
[7] http://susi.theochem.tuwien.ac.at/reg_user/faq/afm.html
[8] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg17307.html
[9] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg03243.html
[10] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg06739.html
[11] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg17516.html
[12] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg18051.html
[13] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg18895.html
[14] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg19462.html
[15] https://publik.tuwien.ac.at/files/PubDat_175934.pdf

On 10/13/2020 4:29 PM, BUSHRA SABIR wrote:
> Hi Wien2k users,
>
> I want to perform AFM calculations for double perovskite oxide La2FeNiO6
> For this, I have a cubic 225-Fm3m structure.
> My question is ..Do I need to flip the spin of Ni only during 
> instgen_lapw -ask?
> or should I make a supercell with two Fe and then choose spin up for 
> one Fe and spin dn for second Fe.
>
> Need help for this
>
> Bushra
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