[QE-users] Magnetic anisotropy energy in magnetic insulators

[Sitangshu Bhattacharya]

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/
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