POTIM: Difference between revisions

Latest revision as of 08:28, 7 April 2022

POTIM = [real]

Default: POTIM	= none,	must be set if IBRION= 0 (MD)
	= 0.5	if IBRION= 1, 2, and 3 (ionic relaxation), and 5 (up to VASP.4.6)
	= 0.015	if IBRION=5, and 6 (as of VASP.5.1)

Description: POTIM sets the time step in molecular dynamics or the step width in ionic relaxations.

For 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.

For IBRION =1, 2, and 3, which corresponds to ionic relaxation using a quasi-Newton algorithm, conjugate-gradient algorithm, and damped molecular dynamics, respectively, the POTIM tag serves as a scaling constant for the step widths. The quasi-Newton algorithm is especially sensitive to the choice of this parameter.

For IBRION = 5, and 6, a phonon calculations using the finite differences approach is done, where POTIM is 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.

Mind: For VASP.5.1 and newer releases, POTIM is automatically reset to 0.015 Å, if the supplied value for POTIM is unreasonably large.

@@ Line 1: / Line 1: @@
 {{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 {{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, and 3 (ionic relaxation), and 5 (up to VASP.4.6)|0.015|if {{TAG|IBRION}}{{=}}5, and 6 (as of VASP.5.1)}}
-Description: {{TAG|POTIM}} sets the time step (MD) or step width scaling (ionic relaxations).
+Description: {{TAG|POTIM}} sets the time step in molecular dynamics or the step width in ionic relaxations.
 ----
-<span>
-{{TAG|IBRION}} = 0:
+* For {{TAG|IBRION}} = 0, {{TAG|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.
-:{{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>
+* For {{TAG|IBRION}} =1, 2, and 3, which corresponds to ionic relaxation using a quasi-Newton algorithm, conjugate-gradient algorithm, and damped molecular dynamics, respectively, the {{TAG|POTIM}} tag serves as a scaling constant for the step widths. The quasi-Newton algorithm is especially sensitive to the choice of this parameter.
-<span>
-{{TAG|IBRION}} =1,2,3:
+* For {{TAG|IBRION}} = 5, and 6, a phonon calculations using the finite differences approach is done, where {{TAG|POTIM}} is the width of the displacement of each ion to calculate the Hessian Matrix.
-: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
+: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.
-</span>
+{{NB|mind| For VASP.5.1 and newer releases, {{TAG|POTIM}} is automatically reset to 0.015 &Aring;, if the supplied value for {{TAG|POTIM}} is unreasonably large.|:}}
-<span>
-{{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.5.1''' and newer releases: if the supplied value for  {{TAG|POTIM}} is unreasonably large, {{TAG|POTIM}} is automatically reset to 0.015 &Aring;.
 </span>
-== Related Tags and Sections ==
+== Related tags and articles ==
 {{TAG|IBRION}}, {{TAG|NFREE}}
-== Example Calculations using this Tag ==
+{{sc|POTIM|Examples|Examples that use this tag}}
-{{TAG|CO on Ni 111 surface}}, {{TAG|CO Vibration}}, {{TAG|Collective jumps of a Pt adatom on fcc-Pt (001): Nudged Elastic Band Calculation}}, {{TAG|H2O molecular dynamics}}, {{TAG|H2O vibration}}, {{TAG|liquid Si}}, {{TAG| Ni 100 surface relaxation}}
 ----
-[[The_VASP_Manual|Contents]]
-[[Category:INCAR]][[Category:Dynamics]]
+[[Category:INCAR tag]][[Category:Ionic minimization]][[Category:Molecular dynamics]][[Category:Phonons]]