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I use vasp 6.4.1.

I need help with noncollinear spin orbit coupling calculation error.
I can't read the wavecar from the collinear run:
ERROR: while reading WAVECAR, plane wave coefficients changed 12318 || 6159

In the normal collinear run, there will be 84 bands.
so I multiply by 2 and set NBANDS = 168 in the noncollinear run.
I see error that the number of bands is different if I only do the above, so I also have to set NBANDS = 168 in the collinear run, right?
I already set ISYM = -1 and set NGX, NGY, NGZ values manually.

But the plane wave coefficients in the noncollinear run are still double than the collinear run.
Would you please let me know what did I miss?


My collinear INCAR:

System = General
LREAL = .FALSE.
NPAR = 4
KPAR = 8
ISIF = 1
LWAVE = .TRUE.
LCHARG = .FALSE.

METAGGA = SCAN
LASPH = .TRUE.
LMIXTAU = .TRUE.
ADDGRID = .TRUE.
ALGO = Normal
NELM = 200
PREC = A

IBRION = -1
NSW = 0
ISYM = -1

EDIFF = 1E-08
ENCUT = 550
ENAUG = 650

NEDOS = 1000
ISMEAR = -5
SIGMA = 0.01
EMIN = 1.23
EMAX = 8.77

LORBIT = 11
ISPIN = 2
LMAXMIX = 6
LMAXTAU = 6

NBANDS = 168

MAGMOM = 4*0 5 -5 5 -5 8*0
AMIX = 0.2
AMIX_MAG = 0.8
BMIX = 0.0001
BMIX_MAG = 0.0001

My Noncollinear INCAR:

System = General
LREAL = .FALSE.
NPAR = 4
KPAR = 8
ISIF = 1
LWAVE = .TRUE.
LCHARG = .FALSE.

METAGGA = SCAN
LASPH = .TRUE.
LMIXTAU = .TRUE.
ADDGRID = .TRUE.
ALGO = Normal
NELM = 200
PREC = A

IBRION = -1
NSW = 0
ISYM = -1

EDIFF = 1E-08
ENCUT = 550
ENAUG = 650

NEDOS = 1000
ISMEAR = -5
SIGMA = 0.01
EMIN = 1.23
EMAX = 8.77

LORBIT = 11
LMAXMIX = 6
LMAXTAU = 6

LSORBIT = .TRUE.
SAXIS = 1 0 0
NBANDS = 168

MAGMOM = 12*0 0 0 5 0 0 -5 0 0 5 0 0 -5 24*0
AMIX = 0.2
AMIX_MAG = 0.8
BMIX = 0.0001
BMIX_MAG = 0.0001

NGX = 42
NGY = 42
NGZ = 54

NGXF = 84
NGYF = 84
NGZF = 108

I attach the OUTCAR files for the collinear and noncollinear runs.
Please help.

-Alpin-

Dear Alpin,

I am not sure if I understand your question properly.
You want to do a non-collinear calculation with spin-orbit coupling?
Is there a special reason why you need to read in the WAVECAR of a collinear calculation?
Because in principle you could just start your calculation from scratch and then you don't have to
read the WAVECAR file.

The vasp wiki has an entry on the NBANDS tag which you can find here:
wiki/index.php/NBANDS
There it is stated that in the non-collinear case the number of bands will be doubled.


I hope this helps to resolve your issue.

All the best Jonathan

Dear Jonathan,

in the LSORBIT wiki, (wiki/index.php/LSORBIT)

The recommended procedure for the calculation of magnetic anisotropies is therefore (please check the section on LMAXMIX):

Start with a collinear calculation and calculate a WAVECAR and CHGCAR file.
Add the tags
LSORBIT = .TRUE.
ICHARG = 11 ! non selfconsistent run, read CHGCAR
LMAXMIX = 4 ! for d-elements increase LMAXMIX to 4, f-elements: LMAXMIX = 6
! you need to set LMAXMIX already in the collinear calculation
SAXIS = x y z ! direction of the magnetic field
NBANDS = 2 * number of bands of collinear run
VASP reads in the WAVECAR and CHGCAR files, aligns the spin quantization axis parallel to SAXIS, which implies that the magnetic field is now parallel to SAXIS, and performs a non selfconsistent calculation. By comparing the energies for different orientations the magnetic anisotropy can be determined. Please mind, that a completely selfconsistent calculation (ICHARG = 1) is in principle also possible with VASP, but this would allow the spinor wavefunctions to rotate from their initial orientation parallel to SAXIS until the correct groundstate is obtained, i.e. until the magnetic moment is parallel to the easy axis. In practice this rotation will be slow, however, since reorientation of the spin gains little energy. Therefore if the convergence criterion is not too tight, sensible results might be obtained even for fully selfconsistent calculations (in the few cases we have tried this worked beautifully).

According to the above wiki page, I should be able to read WAVECAR of collinear calculation to help with convergence and speed up, as written:

The second method also allows to read a preexisting WAVECAR file (from a collinear or non collinear run), and to continue the calculation with a different spin orientation. When a non collinear WAVECAR file is read, the spin is assumed to be parallel to SAXIS (hence VASP will initially report a magnetic moment in the z-direction only).

I have followed the instructions that I can find on this issue (doubling the NBANDS, setting NGX manually, setting ISYM = -1, etc).
Yet, I still couldn't read the WAVECAR.

Hence, I need help to find what INCAR tags that I miss to enable WAVECAR reading in SOC noncollinear calculation.
Please see the OUTCARs attached in the previous message also.

Dear Alpin,

I see. Could you please send me the input files of both of your calculations,
the collinear one and the non-collinear one.
I would need both INCARs, both POSCARs, both KPOINTS files and both POTCAR files.
I will take a look and check what is going wrong.

All the best Jonathan

Dear Jonathan,

I attach the input files here:

jonathan_lahnsteiner2 wrote: ↑Fri Jul 14, 2023 12:37 pm Because in principle you could just start your calculation from scratch and then you don't have to
read the WAVECAR file.

The vasp wiki has an entry on the NBANDS tag which you can find here:
wiki/index.php/NBANDS
There it is stated that in the non-collinear case the number of bands will be doubled.

By the way, if I start the SOC calculation from scratch (no reading WAVECAR), I shouldn't need to set NBANDS and NGX/NGY/NGZ values manually.
Is my understanding correct?

Dear Alpin,

This is correct if you start your calculation from scratch NBANDS, NGX/NGY and NGZ will be set automatically
for you.

All the best Jonathan

Dear Alpin,

I was checking your INCAR files. What I recognized you are setting the NBANDS in both cases the collinear and the non-collinear case to the same values. This might by the reason for the error.
if you strictly follow the vasp wiki your calculation should work:
For the collinear run you have to set in your INCAR file run vasp_ncl
After this you have to change your INCAR file
run vasp_ncl
I also attached a minimal working example for you. This might be of help as well.

All the best Jonathan