spin orbital problem

[ktao]

Hi, everyone,

I want to calculate the magnetic anisotropy energy of a small cluster. I got a really very large MAE value. I doubt the results and suspect there is something wrong in my calculations.

I did MAE calculations as following:

1, I relaxed the structure of the cluster in which all spins are in a collinear configuration

2, I did a non-self consistent calculation with the relaxed structure using "ISPIN = 1 (non magnetic)", and got CHGCAR and WAVECAR files

3, Using saved CHGCAR and WAVECAR, I did a non-collinear calculation (without spin orbital coupling) and got new CHGCAR and WAVECAR files. My input file is as following:

ISTART = 1
NWRITE = 2 : verbosity

ICHARG = 11

ENCUT = 400
ADDGRID = .TRUE.
PREC = accurate : accuracy

NELM = 300 : maximum number of SCF iterations
NELMIN = 8 : minimal number of SCF iterations
NELMDL = -6 : number of non-SCF iterations
EDIFF = 1E-7 : criterion for SCF convergence
ISMEAR = 1 : Methfessel-Paxton smearing
SIGMA = 0.1 : sigma for smearing

NPAR = 1

GGA = PE
GGA_COMPAT = .FALSE.
VOSKOWN = 1

ALGO = Fast

ISPIN = 2
MAGMOM = 0 0 8 7.61 2.47 4 0 8 4 -7.61 2.47 4 -4.70 -6.47 4 4.70 -6.47 4 0 0 8 4.70 6.47 4 -4.70 6.47 4 -7.61 -2.47 4 0 -8 4 7.61 -2.47 4 0 0 8
LNONCOLLINEAR= .TRUE.
LORBIT = 10

NBANDS = 560

# LWAVE = .FALSE.
# LCHARG = .FALSE.

LREAL=.FALSE.

# AMIX = 0.2
# BMIX = 0.00001
# AMIX_MAG = 0.4
# BMIX_MAG = 0.00001
MAXMIX = 40

# Parameters for SOC
ISYM = -1
LMAXMIX = 6
# LSORBIT = .TRUE.
# LORBMOM = .TRUE.
# SAXIS = 0 0 1

# Ionic Relaxation
NSW = 0 : maximum number of ionic steps
EDIFFG = -1.0E-2 : maximal residual force in eV/Ang
IBRION = 1 : quasi-Newton optimization
ISIF = 0 : optimize ions, cell shape and volume

4, I performed a calculation including SOC with saved CHGCAR and WAVECAR from step 3. In the INCAR file I only changed following parameters with SOC calculations,

ISTART = 1
ICHARG = 11

LSORBIT = .TRUE.
LORBMOM = .TRUE.
SAXIS = 0 0 1


5, When the spin direction of the system is along z axis, I only made a small change by setting "MAGMOM = 0 0 8 0 0 8 0 0 8 ...".

As we know, the MAE of most clusters is in the range of 10 meV. However, my results are much larger than that. So, I suspect that there is something wrong in my calculations. Any advices is appreciated. Thank you in advance!

By the way, I put the cluster in a large enough box and did a Gamma point calculation with PBE.

[support_vasp]

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