Requests for technical support from the VASP group should be posted in the VASP-forum.

Difference between revisions of "SPRING"

From Vaspwiki
Jump to navigationJump to search
(Created page with '{{TAGDEF|SPRING|[integer]|-5}} Description: {{TAG|SPRING}} gives the ''spring constant'' between the images as used in the elastic band method ---- {{TAG|SPRING}} has to be s…')
 
Line 26: Line 26:
 
because this can slow down convergence. The default value
 
because this can slow down convergence. The default value
 
usually works quite reliably.
 
usually works quite reliably.
 +
 +
One problem of the nudged elastic band method is
 +
that the constraint (i.e movements only
 +
in the hyper-plane perpendicular to the current tangent) is
 +
non linear. Therefore, the CG algorithm usually fails
 +
to converge, and  we recommended to use
 +
the {{TAG|RMM-DIIS}} algorithm ({{TAG|IBRION}}=1) or the quick-min algorithm ({TAG|IBRION}}=3).
 +
Additionally,
 +
the non-linear constraint (equidistant images) tends to be  violated
 +
significantly during the first few steps (it is only enforced to first order).
 +
If this problem is
 +
encountered, a very low dimensionality parameter ({{TAG|IBRION}}=1, {{TAG|NFREE}}=2)
 +
should be applied in the first we steps, or a steepest
 +
descent minimization without line optimization ({{TAG|IBRION}}=3, {{TAG|SMASS}}=2).
 +
should be used, to  pre-converge the images.
  
 
== References ==
 
== References ==
Line 40: Line 55:
 
== Related Tags and Sections ==
 
== Related Tags and Sections ==
 
{{TAG|IMAGES}}
 
{{TAG|IMAGES}}
 +
{{TAG|IBRION}}
 +
{{TAG|NFREE}}
 +
{{TAG|SMASS}}
  
 
[[The_VASP_Manual|Contents]]
 
[[The_VASP_Manual|Contents]]
  
 
[[Category:INCAR]][[Category:Elastic Band Method]]
 
[[Category:INCAR]][[Category:Elastic Band Method]]

Revision as of 14:46, 11 February 2011

SPRING = [integer]
Default: SPRING = -5 

Description: SPRING gives the spring constant between the images as used in the elastic band method


SPRING has to be set together with IMAGES if the elastic band method is used to calculate energy barriers between two ionic configurations of a system.

For SPRING = 0, each image is only allowed to move into the direction perpendicular to the current hyper-tangent, which is calculated as the normal vector between two neighboring images. This algorithm keeps the distance between the images constant to first order. It is therefore possible to start with a dense image spacing around the saddle point to obtain a finer resolution around this point.

The nudged elastic band method [1][2] is applied when SPRING is set to a negative value e.g.

SPRING = -5

This is also the recommended setting. Compared to the previous case, additional tangential springs are introduced to keep the images equidistant during the relaxation (remember the constraint is only conserved to first order otherwise). Do not use too large values, because this can slow down convergence. The default value usually works quite reliably.

One problem of the nudged elastic band method is that the constraint (i.e movements only in the hyper-plane perpendicular to the current tangent) is non linear. Therefore, the CG algorithm usually fails to converge, and we recommended to use the RMM-DIIS algorithm (IBRION=1) or the quick-min algorithm ({TAG|IBRION}}=3). Additionally, the non-linear constraint (equidistant images) tends to be violated significantly during the first few steps (it is only enforced to first order). If this problem is encountered, a very low dimensionality parameter (IBRION=1, NFREE=2) should be applied in the first we steps, or a steepest descent minimization without line optimization (IBRION=3, SMASS=2). should be used, to pre-converge the images.

References

  1. G. Mills, H. Jonsson and G. K. Schenter, Surface Science, 324, 305 (1995)
  2. H. Jonsson, G. Mills and K. W. Jacobsen, Nudged Elastic Band Method for Finding Minimum Energy Paths of Transitions, in Classical and Quantum Dynamics in Condensed Phase Simulations, ed. B. J. Berne, G. Ciccotti and D. F. Coker (World Scientific, 1998)

Related Tags and Sections

IMAGES IBRION NFREE SMASS

Contents