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Strangely Small Spin Moment in Material with Strong SOC
Date: 2016/04/01 23:03
Name: Keenan

Hello Dr. Ozaki,

I'm in the process of analysing the effect of high magnetic field on the band structure of WTe2. My relevant part of my input file goes as follows:

-----------------------------------------------------------

Species.Number 2

<Definition.of.Atomic.Species
W W9.0-s3p2d2f1 W_CA13
Te Te9.0-s3p3d2f1 Te_CA13
Definition.of.Atomic.Species>

Atoms.UnitVectors.Unit Ang
<Atoms.UnitVectors
3.477 0.00 0.00
0.00 6.249 0.00
0.00 0.00 14.018
Atoms.UnitVectors>

Atoms.Number 12

Atoms.SpeciesAndCoordinates.Unit FRAC
<Atoms.SpeciesAndCoordinates
1 W 0.0 0.60062 0.50000 8.0 4.0 0.0 0.0 0.0 0.0 1 on
2 W 0.0 0.03980 0.01522 8.0 4.0 0.0 0.0 0.0 0.0 1 on
3 W 0.5 0.39938 0.00000 8.0 4.0 0.0 0.0 0.0 0.0 1 on
4 W 0.5 0.96020 0.51522 8.0 4.0 0.0 0.0 0.0 0.0 1 on
5 Te 0.0 0.85761 0.65525 10.0 6.0 0.0 0.0 0.0 0.0 1 on
6 Te 0.0 0.64631 0.11112 10.0 6.0 0.0 0.0 0.0 0.0 1 on
7 Te 0.0 0.29845 0.85983 10.0 6.0 0.0 0.0 0.0 0.0 1 on
8 Te 0.0 0.20722 0.40387 10.0 6.0 0.0 0.0 0.0 0.0 1 on
9 Te 0.5 0.14239 0.15525 10.0 6.0 0.0 0.0 0.0 0.0 1 on
10 Te 0.5 0.35369 0.61112 10.0 6.0 0.0 0.0 0.0 0.0 1 on
11 Te 0.5 0.70155 0.35983 10.0 6.0 0.0 0.0 0.0 0.0 1 on
12 Te 0.5 0.79278 0.90387 10.0 6.0 0.0 0.0 0.0 0.0 1 on
Atoms.SpeciesAndCoordinates>

scf.XcType LSDA-CA # GGA-PBE
scf.SpinPolarization nc
scf.ElectronicTemperature 300.0
scf.energycutoff 300.0
scf.maxIter 200
scf.EigenvalueSolver band
scf.Kgrid 7 7 3
scf.Mixing.Type rmm-diis
scf.Init.Mixing.Weight 0.30
scf.Min.Mixing.Weight 0.001
scf.Max.Mixing.Weight 0.400
scf.Mixing.History 40
scf.Mixing.StartPulay 40
scf.criterion 1.0e-8
scf.spinorbit.coupling on
scf.lapack.dste dstevx

scf.NC.Zeeman.Spin on # on|off, default=off
scf.NC.Mag.Field.Spin 300.0 # default=0.0(Tesla)
scf.Constraint.NC.Spin off # on|off, default=off
scf.NC.Zeeman.Orbital on # on|off, default=off
scf.NC.Mag.Field.Orbital 300.0 # default=0.0(Tesla)

scf.restart on

-----------------------------------------------------------


These calculations are with B=300T (both to the spin and orbital moments).
Surprisingly, the band near the Fermi level is extremely robust due to the B-field.
Giving B=300T yields a slight change (spin moment size on W ~ 0.008 _B, and 0.01 _B for Te), and the band change is almost negligible.

The interesting thing is, while the spin moment almost does not change, the orbital moments for the W and Te increases significantly. Orbital moments for Te, for example, increases up to 1.5 _B, and for W it is about 0.2 _B. Considering the large SOC in W and Te, this small value of spin compared to the orbital momenta is quite strange.

Dr. Ozaki, could you comment on possible reasons for this irregularity? Is it a property of the crystal structure used? Is there a way to instead use the penalty function formalism to overcome this problem?
e
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Re: Strangely Small Spin Moment in Material with Strong SOC ( No.1 )
Date: 2016/04/03 20:15
Name: T. Ozaki

Hi,

> Considering the large SOC in W and Te, this small value of spin compared to the
> orbital momenta is quite strange.

Is there any theorem that the magnitude of spin moment should be comparable to that
of orbital moment in case of a large SOC?
For your case, it seems that the orbital polarization is rather easily induced by the
magnetic field more than the spin polarization, which might be realized by the large band
width and anisotropy of the crystal structure.

Regards,

TO
e

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