restarting from an already optimized structure
flosch... at gmail.com
Sat Mar 8 07:04:21 UTC 2014
usually if you have a properly converged structure and restart with the
identical coordinates CP2K is very happy and will tell you it is converged.
Without your input file with the exact details of your calculation it is
fairly hard to tell what is going on. Nevertheless I will put some random
a) your last structure wasn't perfectly optimized but reached the default
step liimit of 200 steps
b) you use the default cutoff of 280 with elements like N/O/F. For these
elements higher cutoffs (or smoothing) are needed to avoid grideffects
(ripples) on your potential energy surface. If that's the case geometry
optimizations will always have prolems to converge.
c) you use a nonperiodic system and have the CENTER_COORDINATES option on.
In combination with the cutoff problem this leaves you at a different
position w.r.t. the grid points and thus with a different energy which can
be further optimized.
I think b) and c) are most likely. Try a cutoff of 600 and see whether the
problem still exists.
Of course higher cutoffs are expensive but it will give you a smooth PES
and geometry optimizations will need much fewer steps and your ersults are
converged wrt the auxillary basis.
One more comment to your a)
I think the bit about *"non-variational"-ness of the GPW method *you got
from a prevous post from Jürg. He was talking about the convergence of the
plane wave cutoff (better plane wave basis != lower energy). With fixed
settings (basis,...) the GPW energy for a system is variational (lowest
energy = best solution). Therefore forget about that point unless you try
to converge your plane wave basis (which might be an idea, see b) :-))
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