CCL: Problem freezing atoms with gaussian
- From: Ramon Crehuet <rcsqtc() iiqab.csic.es>
- Subject: CCL: Problem freezing atoms with gaussian
- Date: Mon, 19 Sep 2005 16:36:43 +0200
Sent to CCL by: Ramon Crehuet [rcsqtc() iiqab.csic.es]
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Dear CClers,
I am trying to perform an optimisation with gaussian having some
atomic positions fixed. I use Opt=AddRedundant and then the list of
atoms:
4 F
5 F
23 F
etc. After the first step, and 100 iterationsof the kind:
Iteration 6 RMS(Cart)= 0.14928401 RMS(Int)= 0.40589165
Iteration 7 RMS(Cart)= 0.14928401 RMS(Int)= 0.32910240
Iteration 8 RMS(Cart)= 0.14928401 RMS(Int)= 0.25609186
etc
the gaussian output gives: "Curvilinear Step not converged" and stops.
I have two questions. First, on the theoretical side, why does
gaussian
need to iteratively solve a set of equations to fix the position of the
atoms? I understand that this is necessary for non-linear constraints
such as distances or angles, but why for fixing cartesian coordinates?
Is it because in redundant internal coordinates the atomic coordinates
are not linearly related?
And second, can I increase the maximum number of iterations to solve
this system of equations? The default is 100 and I've looked into the
Opt options and some IOp's and couldn't find anything. The system is
quite large, but I do not see why fixing a set of atomic positions can
lead to a unresolvable system. The set of constraints does not seem
incompatible to me. Alternatively, is there a different way to fix some
cartensian atomic positions?
Thanks for your consideration,
Ramon