POTIM: Difference between revisions
(Created page with '{{TAGDEF|POTIM|[real]}} {{DEF|POTIM|none,| ''must'' be set if {{TAG|IBRION}}{{=}} 0 (MD)|0.5| if {{TAG|IBRION}}{{=}} 1,2,3 (ionic relaxation) and 5 (up to VASP.4.6)|0.015|for {{…') |
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{{DEF|POTIM|none,| ''must'' be set if {{TAG|IBRION}}{{=}} 0 (MD)|0.5| if {{TAG|IBRION}}{{=}} 1,2,3 (ionic relaxation) and 5 (up to VASP.4.6)|0.015|for {{TAG|IBRION}}{{=}}5 (up from VASP.5.1)}} | {{DEF|POTIM|none,| ''must'' be set if {{TAG|IBRION}}{{=}} 0 (MD)|0.5| if {{TAG|IBRION}}{{=}} 1,2,3 (ionic relaxation) and 5 (up to VASP.4.6)|0.015|for {{TAG|IBRION}}{{=}}5 (up from VASP.5.1)}} | ||
Description: time (MD) or step width scaling (ionic relaxations) | Description: {{TAG|POTIM}} sets the time step (MD) or step width scaling (ionic relaxations). | ||
---- | ---- | ||
<span> | <span> | ||
{{TAG|IBRION}} = 0 : | {{TAG|IBRION}} = 0: | ||
:{{TAG|POTIM}} gives the time step in all ab-initio Molecular Dynamics runs, it ''has'' to be supplied therefore, otherwise VASP crashes immediately after having started. | :{{TAG|POTIM}} gives the time step in all ab-initio Molecular Dynamics runs, it ''has'' to be supplied therefore, otherwise VASP crashes immediately after having started. | ||
</span> | </span> | ||
<span> | <span> | ||
{{TAG|IBRION}} =1,2,3 | {{TAG|IBRION}} =1,2,3: | ||
: | :In all minimization algorithms (quasi-Newton, conjugate gradient, and damped molecular dynamics) {{TAG|POTIM}} serves as a scaling constant for the step widths. Especially the Quasi-Newton algorithm is sensitive to the choice of this parameter | ||
</span> | </span> | ||
<span> | <span> | ||
{{TAG|IBRION}} = 5 | {{TAG|IBRION}} = 5,6: | ||
: | :In frozen phonon calculations, {{TAG|POTIM}} gives the width of the displacement of each ion to calculate the Hessian Matrix. | ||
:'''VASP.4.6''' and older releases: {{TAG|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.4.6''' and older releases: {{TAG|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 {{TAG|POTIM}} is unreasonably large, {{TAG|POTIM}} is automatically reset to 0.015Å | :'''VASP.5.1''' and newer releases: if the supplied value for {{TAG|POTIM}} is unreasonably large, {{TAG|POTIM}} is automatically reset to 0.015 Å. | ||
</span> | </span> | ||
== Related Tags and Sections == | == Related Tags and Sections == | ||
{{TAG|IBRION}}, | {{TAG|IBRION}}, {{TAG|NFREE}} | ||
---- | |||
[[The_VASP_Manual|Contents]] | [[The_VASP_Manual|Contents]] | ||
[[Category:INCAR]] | |||
Revision as of 11:47, 12 February 2011
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 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.