Which IBRION tag should be used for finite displacement method in calculating Phonons spectrum?

Question

I am planning to use the finite displacement method for calculating phonon spectrum, and I have prepared the INCAR file below to try it on a transition metal trihalide monolayer (e.g., VI$_3$). I would be very grateful if you could please check it and tell me what I should add/omit, and if you recommend following this Phonopy tutorial.

INCAR:

    NPAR = 6
# Self Consistent Calculation step:
ISTART = 0
ICHARG = 2

#Electronic Relaxation:
ENCUT = 550 eV
EDIFF = 1.0E-8
PREC = Accurate
LREAL = .FALSE.
IALGO = 38
ADDGRID=.TRUE.
LCHARG = .FALSE.
LWAVE = .FALSE.

#Phonons
IBRION = -1

#Relaxation:
ISMEAR = 0
SIGMA = 0.05
NSW = 1
GGA_COMPAT = .FALSE.

# Magnetism:
ISPIN= 2
MAGMOM = 4*-5.0 4*5.0 24*0.6
LASPH = .TRUE.
LMAXMIX = 4
VOSKOWN = 1

#Mixer
AMIX     = 0.2
BMIX     = 0.00001
AMIX_MAG = 0.8
BMIX_MAG = 0.00001

I am a little bit confused about which IBRION tag to use (IBRION=-1 or IBRION=6)

Answer 1

Phonopy creates different POSCAR file in which atoms are perturbed, as you are running each POSCAR for NSW=1 or 0, IBRION=-1 will be correct choice. For NSW=1 or 0 , only one self consistency loop will run with no update in ion position , all IBRION tags are equivalent.

IBRION=-1: no update.

The ions are not moved, but NSW outer loops are performed. In each outer loop the electronic degrees of freedom are re-optimized (for NSW>0 this obviously does not make much sense, except for test purposes). If no ionic update is required use NSW=0 instead.