Re: [Wien] How to flip only one atom’s spin in ferromagnetic supercell ?

[Fecher, Gerhard]

Dear Min Lin,
to flip the spin of a particular atom 
first use 
==> 3.“label” an atom (put a 1 in the 3rd column next to the element name) to 
make this atom unique (needed eg. for core-holes)
(maybe you need to create first a P1 cell to have individual access to all 
atoms in the cell, but this you should already have from your supercell 
creation)
then use
==> instgen_lapw during initialisation to set the initial spin direction up or 
down (or edit case.inst)

sgroup will find the changed symmetry using the "numbererd" atoms 
this symmetry is independent on the spin s group just realizes that something 
at this atoms is different, 
the resulting symmetry may be different if you use spin-orbit interaction and 
do not change only up/down but also the spin direction.

Note: it is not necessary that the initial spin orientations (up/down) are kept 
during the scf cycle.

Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."


Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
and
Max Planck Institute for Chemical Physics of Solids
01187 Dresden

Von: Wien [wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von 林敏 
[20520180155...@stu.xmu.edu.cn]
Gesendet: Mittwoch, 18. September 2019 03:01
An: wien@zeus.theochem.tuwien.ac.at
Betreff: [Wien] How to flip only one atom’s spin in ferromagnetic supercell ?

Dear Wien experts,

For special reasons, I need flip only one atom’s spin in ferromagnetic 
supercell.

As we know, non-equivalent atoms will be reduced by “x symmetry” for supercell 
in init_lapw, and this reduction can be prevent by lowering the symmetry. There 
are four methods listed on User’s guide (10.4 Supercell calculations on TiC):

1.delete an atom (to simulate a vacancy)
2.replace an atom by another element (impurity)
3.“label” an atom (put a 1 in the 3rd column next to the element name) to make 
this atom unique (needed eg. for core-holes)
4. displace an atom (for phase transitions or phonons)

In my understanding, these all lower geometry symmetry. So, Lower the symmetry 
of electronic structure (flipping only one atoms’ spin) doesn’t work? Is there 
another method for prohibiting the reduction of number of non-equivalent atoms?

I really appreciate if any suggestions.

———
Min Lin
2018 Ph. D student
Physical Chemistry
Chemistry Department Chemistry & College of Chemistry and Chemical Engineering
Xiamen University
China
e-mail: lin...@stu.xmu.edu.cn
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[Wien] How to flip only one atom’s spin in ferromagnetic supercell ?

[林敏]

Dear Wien experts,

For special reasons, I need flip only one atom’s spin in ferromagnetic 
supercell.

As we know, non-equivalent atoms will be reduced by “x symmetry” for supercell 
in init_lapw, and this reduction can be prevent by lowering the symmetry. There 
are four methods listed on User’s guide (10.4 Supercell calculations on TiC):

1.delete an atom (to simulate a vacancy) 
2.replace an atom by another element (impurity) 
3.“label” an atom (put a 1 in the 3rd column next to the element name) to make 
this atom unique (needed eg. for core-holes)
4. displace an atom (for phase transitions or phonons)

In my understanding, these all lower geometry symmetry. So, Lower the symmetry 
of electronic structure (flipping only one atoms’ spin) doesn’t work? Is there 
another method for prohibiting the reduction of number of non-equivalent atoms?

I really appreciate if any suggestions.


———
Min Lin
2018 Ph. D student
Physical Chemistry 
Chemistry Department Chemistry & College of Chemistry and Chemical Engineering
Xiamen University
China
e-mail: lin...@stu.xmu.edu.cn___
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[Wien] Odd result (that may be correct)

[Laurence Marks]

I have an odd result that is probably correct; hopefully someone has come
across the relevant physics before and can give me a clue.

The case is complicated. I have a rocksalt structure (389 atom supercell)
based upon NiO with 2Cr3+ substituted for 3Ni2+ semirandomly, calculated
with -eece 0.25 for Ni & Cr, and closely following antiferromagnetic
ordering. As it was semirandomly generated, it is not exactly
antiferromagnetic, and the unit has a nett moment of -2. It is a decent
insulator.

When analyzing the EELS spectra of the Ni L (no core hole), there is a
~0.8eV shift to higher energy in the first peak for the Ni atoms with +2
spin (~1.72 inside the RMT) relative to those with -2 spin. This seems to
"make sense" as an exchange energy of the unoccupied states with the mean
spin of the unit cell. (It is not related to the core states, so can only
be the unoccupied states.) Does this ring a bell with anyone?

-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
Corrosion in 4D: www.numis.northwestern.edu/MURI
Co-Editor, Acta Cryst A
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
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