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POTIM = [real] 

Default: POTIM = none, must be set if IBRION= 0 (MD)
= 0.5 if IBRION= 1,2,3 (ionic relaxation) and 5 (up to VASP.4.6)
= 0.015 for IBRION=5 (up from VASP.5.1)

Description: POTIM sets the time step (MD) or step width scaling (ionic relaxations).


POTIM gives the time step (in fs) in all ab-initio Molecular Dynamics runs, it has to be supplied therefore, otherwise VASP crashes immediately after having started.

IBRION =1,2,3:

In all minimization algorithms (quasi-Newton, conjugate gradient, and damped molecular dynamics) POTIM serves as a scaling constant for the step widths. Especially the Quasi-Newton algorithm is sensitive to the choice of this parameter.

IBRION = 5,6:

In frozen phonon calculations, POTIM gives the width of the displacement of each ion to calculate the Hessian Matrix.
VASP.4.6 and older releases: POTIM has to be small enough to ensure that the displacements are within the harmonic limit. The vibrational frequencies using the frozen phonon approach are based on the harmonic approximation.
VASP.5.1 and newer releases: if the supplied value for POTIM is unreasonably large, POTIM is automatically reset to 0.015 Å.

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