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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).
IBRION = 0:
- 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.
- 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.