Within all relaxation algorithms (IBRION=1,2 and 3) the parameter POTIM should be supplied in the INCAR file. For IBRION0, the forces are scaled internally before calling the minimization routine. Therefore for relaxations, POTIM has no physical meaning and serves only as a scaling factor. For many systems, the optimal POTIM is around 0.5. Because the Quasi-Newton algorithm and the damped algorithms are sensitive to the choice of this parameter, use IBRION=2, if you are not sure how large the optimal POTIM is.

SYSTEM = Mg-hex
ENCUT = 250
ISTART = 0; ICHARG = 2
ISMEAR = 1; SIGMA = 0.2
NSW = 60; IBRION = 2
ISIF = 3
POTIM = 0.2
EDIFF = 1E-6; EDIFFG = -1E-3
PREC = Accurate