[QE-users] Magnetic anisotropy energy in magnetic insulators

[Sitangshu Bhattacharya]

Sorry for the typo: I meant a "collinear". And the cell consist of two same
atoms.

Regards,
Sitangshu


On Sun, Nov 10, 2019 at 5:22 AM Sitangshu Bhattacharya <
sitangshu at iiita.ac.in> wrote:

> Dear QEusers,
>
> Recently, I came across the force theorem concept (Phys. Rev. B 90, 205409
> (2014)) to determine the magnetic anisotropy energy (MAE) in magnetic
> metals. After a basic understanding of the physics and workflow for
> magnetic metals, I tried to execute the same for magnetic insulators (with
> a gap). I am bit confused here as the workflow process is not mentioned
> clearly anywhere (after googling tons of links in user-list) for magnetic
> insulators.
>
> So, here the problem is: I have constructed a reduced dimensional crystal
> with incomplete p orbitals. The cell has two atoms. I am expecting a strong
> MAE as I have checked that the crystal is found to possess a strong SOC.
> So the first step: I did a non-collinear and non-spin orbit computation
> using a scalar relativistic pseudo to figure out the spin polarized charge
> densities. Now here is the problem.
> The input snippet, I used is:
>  &system
>            nspin = 2
>            tot_magnetization=3
>            occupations='smearing'
>            smearing='marzari-vanderbilt'
>            degauss=0.005
>
> The out snippet at the end is obtained as
>      total magnetization       =     3.00 Bohr mag/cell
>      absolute magnetization    =     3.01 Bohr mag/cell
>
>      Magnetic moment per site:
>      atom:    1    charge:   12.7978    magn:    0.6984    constr:
>  0.0000
>      atom:    2    charge:   12.7978    magn:    0.6984    constr:
>  0.0000
>
> Is this the correct flow to get the charge density for magnetic insuators?
> Interestingly,
> 1) The good news is that the above calculation converges!
> But,
> 2) The moments changes if I change tot_magnetization=1.
> 2) If I use starting_magnetization(1) = say 1, then at the end, the
> magnetization and moments are converged to zero with occupation=smearing.
> 4) If I use occupations=fixed, the charge densities are not properly
> calculated and produces error in the HOMO LUMO energy positions.
>
> I am clueless to what is happening! I would be glad for any response!
>
> With regards,
> Sitangshu Bhattacharya
> IIIT-Allahabad, India
>
> **********************************************
> Sitangshu Bhattacharya (সিতাংশু ভট্টাচার্য), Ph.D
> Assistant Professor,
> Room No. 2221, CC-1,
> Nanoscale Electro-Thermal Laboratory,
> Department of Electronics and Communication Engineering,
> Indian Institute of Information Technology-Allahabad
> Uttar Pradesh 211 012
> India
> Telephone: 91-532-2922000 Extn.: 2131
> Web-page: http://profile.iiita.ac.in/sitangshu/
> Institute: http://www.iiita.ac.in/
>
>

-- 
**********************************************
Sitangshu Bhattacharya (সিতাংশু ভট্টাচার্য), Ph.D
Assistant Professor,
Room No. 2221, CC-1,
Nanoscale Electro-Thermal Laboratory,
Department of Electronics and Communication Engineering,
Indian Institute of Information Technology-Allahabad
Uttar Pradesh 211 012
India
Telephone: 91-532-2922000 Extn.: 2131
Web-page: http://profile.iiita.ac.in/sitangshu/
Institute: http://www.iiita.ac.in/
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