From VASP Wiki

NSW = [integer]
Default: NSW = 0 

Description: NSW sets the maximum number of ionic steps.


NSW gives the number of steps in all ab-initio Molecular Dynamics runs, it has to be supplied therefore, otherwise VASP crashes immediately after having started.

IBRION != 0:

In all minimization algorithms (quasi-Newton, conjugate gradient, and damped molecular dynamics) NSW defines the maximum number of ionic steps.

Mind: Within each ionic step at most NELM electronic-SC loops are performed unless the EDIFF convergence criterium is matched before. Exact Hellmann-Feynman forces and stresses are calculated for each ionic step.

Examples that use this tag