My Community

Dear all,
My problem is surface relaxation with the following INCAR file:

NELMIN = 4
MaxMix = 60
IALGO = 48
ENCUT = 320
LREAL = AUTO
EDIFF = 1E-04
IBRION = 2
ISIF = 3
NSW = 40
ISYM = 2
NELMDL = -4
ISMEAR = 1
SIGMA = 0.1
NPAR = 6
LPLANE = TRUE
NSIM = 4

By increasing the size of the supercell (90 ions) the convergency become difficult. When KPOINTS is (11x11x1), the surface relaxation doesn't converge until 40th ionic steps!! In fact magnitudes of ENERGY fluctuate. Despite, the same problem with KPOINTS (9x9x1) converges at 30th ionic step.
It is important to mention that these difficulties do not happen when the supercell has 40 ions.

I will be very grateful for any help, any idea.

I don't think it is a reason to worry if it takes 40 ionic steps until convergence is reached. I have worked with slabs that needed over 100 ionic steps.