Hello VASP community,

I'm running into an issue with my band structure calculations for FeS₂ pyrite (1 cubic unit cell, 12 atoms) where the resulting bands appear non-smooth and zigzag-like (see attached plot). Despite tweaking several INCAR parameters, I haven’t been able to resolve the problem.

Calculation Details:

• System: FeS₂ pyrite, cubic unit cell (12 atoms)
• KPOINTS: 6×6×6 Monkhorst-Pack grid
• INCAR: See below (full file attached)
• Attachments: Band structure plot, INCAR file

Troubleshooting Steps Taken:

• Increased k-point density — minimal improvement observed
• Adjusted SIGMA between 0.05 and 0.15 eV — no effect
• Used GGA-PBE functional (no hybrid functionals)
• DFT+U applied (U = 1.5 eV for Fe)
• ICHARG = 11, ALGO = Normal, NELM = 1 (non-SCF calculation using CHGCAR from prior SCF step)

Questions:

I'm happy to provide additional files (POSCAR, KPOINTS, etc.) if needed. Thank you for your time and expertise!

INCAR (excerpt):

SYSTEM = fes2_bands

NCORE = 2

GGA = PE

ISTART = 0

ICHARG = 11

NBANDS = 60

ALGO = Normal

PREC = Accurate

NELM = 1

ENCUT = 400.0

EDIFF = 1e-06

ISMEAR = 0

SIGMA = 0.05

NSW = 0

IBRION = -1

ISIF = 2

ISPIN = 1

LORBIT = 11

LCHARG = .FALSE.

LWAVE = .FALSE.

#DFT + U settings:

LDAU = .TRUE.

LDAUTYPE = 2

LDAUL = 2 -1

LDAUU = 1.5 0

LDAUJ = 0 0

LMAXMIX = 4

LDAUPRINT = 1