[QE-users] Magnetic anisotropy energy in magnetic insulators

[BARRETEAU Cyrille]

Dear Sitangshu

You should have a look at the example (in PP) on how to use the FT to extract the magnetic anisotropy energy and its orbital/site decomposition. FT ca be applied to insulators as well as metals.

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.205409
https://iopscience.iop.org/article/10.1088/1367-2630/ab3060/pdf
https://arxiv.org/abs/1907.04532
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.93.144405

You should 1st perform a scf  collinear calculation and then two nscf non-collinear (+SOC) calculations starting from previous scf. Then use projwfc (with correct input) to extract the MAE and site/orbital decomposition.

best
Cyrille

ps: use recent versions of pw (>6.2)

========================
Cyrille Barreteau
CEA Saclay, IRAMIS, SPEC Bat. 771
91191 Gif sur Yvette Cedex, FRANCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+33 1 69 08 38 56 /+33  6 47 53 66 52  (mobile)
email:     cyrille.barreteau at cea.fr
Web:     http://iramis.cea.fr/Pisp/cyrille.barreteau/
========================
________________________________
De : users [users-bounces at lists.quantum-espresso.org] de la part de Sitangshu Bhattacharya [sitangshu at iiita.ac.in]
Envoyé : dimanche 10 novembre 2019 08:30
À : Quantum Espresso users Forum
Objet : Re: [QE-users] Magnetic anisotropy energy in magnetic insulators

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<mailto: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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