Subject: Fwd: CPCM optimisation

From: "warau kimura" <[email-masked]>
Date: Thu, 27 Jun 2002 14:33:49 +0900

Hello,

I am very thankful Dr.Emrys Thomas for replying my question about CPCM 
optimisation. I forward his answer here.

Best wishes,

Kimura

From: [email-masked]
To: [email-masked]
Subject: Re: CPCM optimisation
Date: Wed, 26 Jun 2002 14:55:51 +0100

I have met this problem so many times (even with molecules < 15
atoms)that I do not regard CPCM as a viable model except of
course for rigid geometries.Here is some advice I recieved recently:
"When using CPCM one quite often run into optimisation problems
dealing with more complex systems. You may overcome the problem by a
partial optimisation followed by a full optimisation. Usually the 
convergence problem is related to the 'max force'. If this is the case then 
you can identify the degree of freedom, which is related to this max force. 
In the partial
optimisation you should freeze this parameter - usually a dihedral angle. If 
the 'max force'is related to a heteroatom or chemical group it may be
advantageous to freeze all geometric parameters related to this heteroatom 
or heavy atoms in the group.
Sometimes this procedure requires a couple of partial optimisations but we
succeeded in the end. If this doesn't help you may try to change different
parameters related to the solvation model, e.g. increase the number of
tesserae, change the partial charges (hereby change the atomic spheres) in
an initial optimisation followed by an optimisation using default partial
charges".
In my experience the unsophisticated Onsager model in G98
always converges during optimisations.You could also check out
GAMSOL3.0,which incorporates AMSOL into GAMESS(US) [with
excellent documentation] and allows optimisations and frequency
calculations at HF/6-31G* and HF/6-31+G* levels.
Best wishes
Emrys Thomas

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