[CP2K:5047] Re: restarting from an already optimized structure

[SRKC Sharma Yamijala]

Dear Dr. Flo,

Thank you for the information. Among the points which you have raised, I
indeed did the point 'C'. Sorry for not giving the sufficient information
in previous post. Here in, I have attached the input file and the energy as
a function of the optimization step, which shows it is pretty much
converged.

So, do I need to switch off the " CENTER_COORDINATES" option after getting
an optimized structure if I want to perform a single point energy
calculation?

I have used a cutoff of 320 Ry and I also found that I cannot run all my
systems (minimum 290 atoms and maximum 830 atoms with a cutoff of even 450
Ry) on the machines which are available for me.

Thanking you for your immediate response,
Sincerely,
Chaitanya Sharma.

P.S: Please let me know, if I need to give any more information to identify
the exact problem.








********************************************************
*Chaitanya Sharma,*
*Prof. Bala and Prof. Pati'*s groups,
Chemistry and Physics Materials unit,
JNCASR, BANGLORE,
Lab:: (080-2208) 2581, 2809
https://sites.google.com/site/sharmasrkcyamijala/
*********************************************************


On Sat, Mar 8, 2014 at 12:34 PM, Florian Schiffmann <flosch... at gmail.com
> wrote:

> Dear Chaitanya,
>
> 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
> guesses on.
>
> 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) :-))
>
> Cheers
> Flo
>
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