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I want to calculate spin-orbit coupling, taking Si for example.
I follow the procedures in manual which says:
(http://cms.mpi.univie.ac.at/vasp/vasp/LSORBIT_tag.html)
-------------------------------------
* 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: 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
.......
--------------------------------------


What I do has two steps:

1. Do a collinear calculation, using the following INCAR file:
#---------------INCAR collinear------------
system = Si

ISTART=0
ICHARG=2
ENCUT=250
EDIFF=1e-4
ISMEAR=-5

ISPIN=2

LMAXMIX=4
NBANDS=18
ISYM=0
#-----------------------------------------

Run vasp to reach convergence.

2. Add spin-orbit coupling tags to the INCAR file, the changed INCAR file is as follow:
#---------------INCAR lsorbit--------------
system = Si

ISTART=1
ICHARG=11
ENCUT=250
EDIFF=1e-4
ISMEAR=-5

LSORBIT=T
SAXIS=0 0 1

LMAXMIX=4
NBANDS=18
ISYM=0
#-----------------------------------------

However, when I run vasp in the same directory again, error occurs!

#---------------error information-----------------
vasp.5.2.2 15Apr09 complex
POSCAR found : 1 types and 2 ions
LDA part: xc-table for Pade appr. of Perdew
found WAVECAR, reading the header
number of k-points has changed, file: 260 present: 512
trying to continue reading WAVECAR, but it might fail
WARNING: stress and forces are not correct
POSCAR, INCAR and KPOINTS ok, starting setup
WARNING: small aliasing (wrap around) errors must be expected
FFT: planning ...( 1 )
reading WAVECAR
ERROR: while reading WAVECAR, plane wave coefficients changed 678
339
#-------------------------------------------------


THREE QUESTIONS:

1. Why the k-points changed when LSORBIT is set true?
The KPOINS file is all the same.
#-------KPOINTS--------
Auto
0
Gamma centered
8 8 8
0 0 0
#----------------------

2. Why plane wave coefficients changed when LSORBIT is set true?

3. Are there something wrong in my operations?
Or is the method discribed in the manual wrong?
How to do a spin-orbit coupling calculation?

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