Subject: Re: CCL:Failing optimization (1 imag. freq)

From: [email-masked] (Alain Kessi)
Date: Tue, 28 Jan 1997 16:06:36 +0100

Maybe the following suggestion is too obvious, and you've probably already
done this, but since I cannot imagine how it could fail, I'll mention it
anyway: take a step into the direction corresponding to your negative
curvature (imaginary frequency) and start your optimization again there.
The point is that you need to break your symmetry explicitely, not only
switch the symmetry off, since at a point of symmetry you'll never have
a gradient to break the symmetry, except by numerical imprecision. If the
more sophisticated algorithms using internal coordinates don't work, just
do a simple Cartesian optimization. This cannot fail, basically, except
if you take too large steps, which might happen depending on the curvature.
The energy should be lower when you take the first step (by hand), and
the optimizer should have no problems further lowering it. A slow method
which really cannot fail, given small enough steps, is following the
gradient (steepest descent).

Hope this helps,

Alain

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From: A J Turner <[email-masked]>
Date: Tue, 28 Jan 1997 17:35:15 +0000 (GMT)

Hi!

Why not take a IRC down the negative eign value?

Best wishes

Alex

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|Alexander J Turner         [email-masked]                  |
|Post Graduate              |http://www.bath.ac.uk/~chpajt/home.html|
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|University of Bath         |                                       |
|Bath, Avon, U.K.           |Field: QM/MM modeling                  |
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