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Hello all,

I set up a calculation for a Fe dimer with spin-orbit coupling starting from the geometry and charge density of a collinear calculation. Everything goes on fine but at the end it gives me that the easy axis is along the perpendicular (x) direction to the dimer axis. Am I doing something wrong or is it just a matter of misunderstanding the VASP results? Here is the input file for the SOC calculation along the z axis:

SYSTEM = Fe2
LWAVE = .TRUE.
LCHARG = .FALSE.
ISPIN = 2
LMAXMIX = 4
IBRION = 2
NSW = 250
NELM = 250
NELMDL = 6
EDIFF = 0.00000001
EDIFFG = -0.005
PREC = Accurate
ENMAX = 575
AMIX = 0.2
BMIX = 0.0001
AMIX_MAG = 0.8
BMIX_MAG = 0.0001
ISMEAR = 0
SIGMA = 0.02
NBANDS = 40
RWIGS = 0.98
ADDGRID = .TRUE.
LORBIT = 11
ALGO = Fast
NPAR = 8
NSIM = 8
LSORBIT = .TRUE.
ICHARG = 1
ISYM = 0
SAXIS = 0 0 1
MAGMOM = 0 0 3 0 0 3
LORBMOM = .TRUE.

And here is for the x axis:

SYSTEM = Fe2
LWAVE = .TRUE.
LCHARG = .FALSE.
ISPIN = 2
LMAXMIX = 4
IBRION = 2
NSW = 250
NELM = 250
NELMDL = 6
EDIFF = 0.00000001
EDIFFG = -0.005
PREC = Accurate
ENMAX = 575
AMIX = 0.2
BMIX = 0.0001
AMIX_MAG = 0.8
BMIX_MAG = 0.0001
ISMEAR = 0
SIGMA = 0.02
NBANDS = 40
RWIGS = 0.98
ADDGRID = .TRUE.
LORBIT = 11
ALGO = Fast
NPAR = 8
NSIM = 8
LSORBIT = .TRUE.
ICHARG = 1
ISYM = 0
SAXIS = 1 0 0
MAGMOM = 0 0 3 0 0 3
LORBMOM = .TRUE.

The calculation with the quantization axis along the z axis gives the following results:

FREE ENERGIE OF THE ION-ELECTRON SYSTEM (eV)
---------------------------------------------------
free energy TOTEN = -9.446615 eV

energy without entropy= -9.446615 energy(sigma->0) = -9.446615

orbital moment (x)

# of ion p d tot
----------------------------------------
1 0.000 0.000 0.000
2 0.000 0.000 0.000
----------------------------------------
0.000 0.000 0.000



orbital moment (y)

# of ion p d tot
----------------------------------------
1 0.000 0.000 0.000
2 0.000 0.000 0.000
----------------------------------------
0.000 0.000 0.000



orbital moment (z)

# of ion p d tot
----------------------------------------
1 0.000 0.130 0.130
2 0.000 0.130 0.130
----------------------------------------
0.000 0.260 0.260

magnetization (x)

# of ion s p d tot
----------------------------------------
1 0.000 0.000 0.000 0.000
2 0.000 0.000 0.000 0.000
------------------------------------------------
tot 0.000 0.000 0.000 0.000



magnetization (y)

# of ion s p d tot
----------------------------------------
1 0.000 0.000 0.000 0.000
2 0.000 0.000 0.000 0.000
------------------------------------------------
tot 0.000 0.000 0.000 0.000



magnetization (z)

# of ion s p d tot
----------------------------------------
1 0.048 -0.006 2.776 2.818
2 0.048 -0.006 2.776 2.818
------------------------------------------------
tot 0.097 -0.012 5.553 5.637

while the calculation along the perpendicular (x) direction gives:

FREE ENERGIE OF THE ION-ELECTRON SYSTEM (eV)
---------------------------------------------------
free energy TOTEN = -9.447210 eV

energy without entropy= -9.447210 energy(sigma->0) = -9.447210

orbital moment (x)

# of ion p d tot
----------------------------------------
1 -0.001 0.080 0.080
2 -0.001 0.080 0.080
----------------------------------------
-0.001 0.161 0.160



orbital moment (y)

# of ion p d tot
----------------------------------------
1 0.000 0.000 0.000
2 0.000 0.000 0.000
----------------------------------------
0.000 0.000 0.000



orbital moment (z)

# of ion p d tot
----------------------------------------
1 0.000 0.000 0.000
2 0.000 0.000 0.000
----------------------------------------
0.000 0.000 0.000

total charge

# of ion s p d tot
----------------------------------------
1 0.478 0.095 6.388 6.961
2 0.478 0.095 6.388 6.961
------------------------------------------------
tot 0.955 0.191 12.776 13.922



magnetization (x)

# of ion s p d tot
----------------------------------------
1 0.000 0.000 0.000 0.000
2 0.000 0.000 0.000 0.000
------------------------------------------------
tot 0.000 0.000 0.000 0.000



magnetization (y)

# of ion s p d tot
----------------------------------------
1 0.000 0.000 0.000 0.000
2 0.000 0.000 0.000 0.000
------------------------------------------------
tot 0.000 0.000 0.000 0.000



magnetization (z)

# of ion s p d tot
----------------------------------------
1 0.048 -0.006 2.776 2.818
2 0.048 -0.006 2.776 2.818
------------------------------------------------
tot 0.097 -0.012 5.551 5.636


Thank you for you kind help.

- Jose Luis

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