CG vs BFGS optimizer

[Tobias Kraemer]

Dear all,


I was wondering if someone could clarify for which system size the CG 
optimizers should be preferred over BFGS?
The manual states that CG is "OK for large systems", while BFGS is "most 
efficient for 'small' systems". 
One of my systems contains 520 atoms, and I have tried both optimizers, on 
the same starting structure. While 
BFGS converged within 40 geometry optimisation cycles (~15 hrs walltime), 
CG is still going (started at same time).
It is showing signs of convergence though, which is  good. So I understand 
that BFGS is much more efficient in this
particular case. Is there a rule of thumb for the system size in terms of 
number of atoms?

Another question in the context of geometry optimisations, is there a way 
to output both the cell axis along with the current
geometry of the model? The xyz does not contain info about the cell axis, 
while I seem to be unable to analyse each
step of the optimiation if I set the format in the output to pdb. Is there 
a viewer which could show both (essentially showing the
individual structures during the geometry optimisation steps and the cell 
axis).

Your answers are much appreciated ....


Best


Tobias

 
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