[Wien] Magnetocrystalline anisotropy

[Xavier Rocquefelte]

Dear Jaroslav

Thank you for your quick and detailled reply.

It seems to me that there is one important difference between my 
calculations and yours.

Indeed, my calculations are done using P1 symmetry. In addition, the 
unit cell for FM and AFM1 magnetic orders are exactly the same. I only 
modify the case.inst file. Thus if we have a problem of local rotation 
matrix it should appear in both cases. However, it seems that the 
problem only appear in the case of AFM order calculation. I never had 
curious MAE for FM calculations.

I should admit that when estimating MAE for FM we have energies larger 
of one order of magnitude compared to AFM ones.
However, as shown in the previous document we have no noise in our 
calculated MAE values in both FM and AFM cases, suggesting that these 
calculations are already converged.

The problem seems to be still opened to suggestions but I will look at 
your idea in more details in the afternoon.

Thank you again

Cheers

Xavier





Le 09/01/2018 à 10:49, Jaroslav Hamrle a écrit :
> Dear Xavier,
>
> your problem somewhat resembles me my problem I had when calculating 
> magnetic linear dochroism (MLD) on bcc Fe. The similarity is that we 
> both want to see small changes in electronic structure when rotating 
> magnetic field direction.
>
> What help me:
> 1) run fine convergence criteria, such as runsp_lapw -p -cc 0.000001 
> -ec 0.000001
>
>
> 2) as suggested Prof. Blaha, it was important to increase k-mesh (in 
> my case up to 100), and apply fine BZ integration (TEMP or TEMPS) with 
> small value as 0.001, not default TETRA.
> for example change case.in2 by using command
> sed '3s/^................/TEMP    0.001   /' $file.in2 > 
> $file.in2_TEMPnew
> more here"
> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg16815.html 
>
> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg16844.html 
>
>
>
> 3) for some magnetization direction, I had problem with either wrong, 
> either suspicious values of local rotation matrix,
> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg16894.html 
>
>
> Problem was that for some external magnetization directions, the local 
> direction of magnetization was not [001].
> In one case (external M along [-111]), the local magnetization 
> direction was [-0.94281 0   -0.33333] which I think is not correct, 
> and MLD was wrong too.
> In some case, local magnetization direction was along x or along y, 
> which I dont know if it is correct. On one hand, eigenenergies agreed 
> perfectly, but anyway I saw small change in MLD in those cases.
>
> But as a blind suggestion for you, try if local rotation matrices are 
> correct. Namely try if
> mag_glob*R = mag_loc
> where mag_glob is your (external i.e. in global coordinates) 
> magnetization direction, R is local rotation matrix for each atom (can 
> be found in case.struct or case.outsymso) and mag_loc is local 
> magnetization direction, which in my (maybe naive and wrong) 
> understanding should be [001].
>
> Hoping it helps
> With my best regards
>
> Jaroslav
>
>
> On 09/01/18 09:44, Xavier Rocquefelte wrote:
>> Dear Colleagues
>>
>> I recently obtained a surprising result concerning the calculation of 
>> the magnetocrystalline anisotropy energy (MAE) of SeCuO3.
>>
>> This compound has a monoclinic symmetry (SG. P21/n) and is known to 
>> be antiferromagnetically ordered at low temperature.
>>
>> Here I provide the results obtained for two magnetic orders, named FM 
>> and AFM1 (see attached document) :
>>
>> https://filesender.renater.fr/?s=download&token=1da93a22-9592-3a7e-ba2e-1533fcae45d2 
>>
>>
>> These calculations have been done using WIEN2k_17, GGA = PBE, RKMAX = 
>> 6, kmesh = 5 4 4 and in P1 symmetry. The results are the same using 
>> RKMAX = 7.
>>
>> The AFM1 order is the more stable one, as expected.
>>
>> However, as shown in the document the MAE of AFM1 order is not 
>> symmetric, which is not expected. In contrast the MAE for FM order is 
>> symmetric.
>>
>> Based on the recent discussion "zigzag potential", it seems to me 
>> that the AFM1 MAE should be symmetric, because the magnetic moment is 
>> a pseudo-vector. Is it possible that the present problem is related 
>> to the fact that in the present implementation of the spin-orbit 
>> coupling we neglect the off-diagonal terms? Do you have any idea 
>> about the problem we are facing? Does someone observe such unusual 
>> MAE for other systems?
>>
>> Best Regards
>>
>> Xavier
>>
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