Subject: Summary of MOPAC 6.0 C.I.Convergence Question

From: <[email-masked]>
Date: Thu, 3 Nov 94 13:11 CST

Hello again,

I recently posted a request for suggestions on achieving convergence in MOPAC 6
configuration calculations, to which I recieved to following replies.  I am in
the process of trying some of the ideas out and if anyone is interested I can
let them know what worked the best.  One additional question: who distributes
MOPAC 93 and what does it cost?  I've seen MOPAC 7 on www.ccl.net but
have not been able to locate MOPAC 93.  At any rate, here are the responses.
Thanks again to all who replied.

Kristopher Wise
Univeristy of Oklahoma
Department of Chemistry and Biochemistry
[email-masked]

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From:	IN%"[email-masked]"  2-NOV-1994 05:02:33.94
To:	[email-masked]
CC:	
Subj:	

I am NOT sure if MOPAC 6.0 does correctly C.I>
As I know in MOPAC 93 ( or MOPAC 7) people changed much in the code
calculating C.I. 
So try to use newer version or at least conntac Dr Stewart ( the author 
of MOPAC )
Best wishes
G.Bakalarski (Poland)

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From:	IN%"[email-masked]"  "Frank Jensen"  1-NOV-1994 06:09:47.65
To:	[email-masked]
CC:	
Subj:	mopac ci optimizations

	A couple of points:
	1) Do you really need geometries converged to less than 1.0 kcal/mol?
The energy should be stable to ~ 0.01 kcal/mol with a grad.norm of this size.
Relative energies of "accuracies" of 0.01 kcal/mol has no meaning in semiempirical
calculations, the inherent error is much larger.
	2) If you really need this tight convergence, ypu need to take care
that the gradients actually are calculated to an accuracy which allows small
steps, i.e. convergence to less than 1.0 may involve geometry steps of maybe
0.0001 Ang or less. Make sure that gradients are actually calculated sufficiently
accurate, i.e. tighten up the SCF convergence and use the analytical CI gradient
option.
	3) EF will work if you provide it with a good Hessian, specifying
HESS=1 will calculate the Hessian at the first step. This is expensive at the
CI level, you may try to use a Hessian from the RHF wave function, and just
read it in for use at the CI level.
	4) if these options do not work, I'll be happy to take a look at your
problem.

	Frank

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From:	IN%"[email-masked]"  "Matthew E. Harbowy" 31-OCT-1994 23:12:58.09
To:	[email-masked], [email-masked]
CC:	
Subj:	CCL:Convergence in MOPAC C.I. calculations

>I am using MOPAC 6.0 to do calculations on fairly large polycyclic
>molecules related to porphyrins.  Part of this work involves optimizing
>geometries and calculating energies for the cations and anions of these
>molecules.  To make these calculations more accurate (hopefully) we are
>using the configuration interaction options in MOPAC 6, but have encountered
>some problems with convergence.  After reducing the gradient to below 1.0,

It's a great idea, one that i've tried to rationalize myself. It's also
a double correction, since parameterization adjusts the energies to 
include the 'correlation' piece once already, and what that means for
transition states is anyone's guess.

>the optimization begins to oscillate, and shows no sign of convergence
>after running for several hours.  A typical command line is as follows:
>
>AM1 PRECISE CHARGE=-1 C.I.=(4,2) VECTORS NODIIS

Indeed, I saw the same thing, and EF only makes it worse. NLLSQ was the
one that did the trick, and occasionally I would use SIGMA as well. Also,
you have to be very careful about picking your ci levels. sometimes (5,2)
is a much better choice due to near degeneracies which don't cause it
to abort with errors, but oscillate instead. 

Also, try dummy atoms, and define your geometries in different ways. A
well chosen zmatrix cured some, not all, of my ills. Part of my problem
turned out to be I was attributing more symmetry to the molecule than was 
true by a bad zmatrix definition. XYZ was right out because I was studying
a cyclization, and the orchestrated nature of the reaction required good
control of the zmatrix. I assume for porphyrin analogs you're using 
symmetry to cut down on the number of dependent variables. what I found was 
the forced symmetry led me to a multiple saddle point, not a minimum or
transition state.

>Kristopher Wise
>University of Oklahoma
>Department of Chemistry and Biochemistry
>[email-masked]

matt harbowy
tea chemist, thomas j lipton.
-- 
matt harbowy               |  
[email-masked]        | "I'm the bear that went
[email-masked]  |  over the mountain."
[email-masked]            |

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From:	IN%"[email-masked]" 31-OCT-1994 14:06:18.73
To:	[email-masked]
CC:	
Subj:	Re:  CCL:Convergence in MOPAC C.I. calculations

Hello Kristopher,

I don't think that the analytical CI gradients really work in  
MOPAC 6.0.  Please try the NOANCI keyword.  This should give
you better gradients.

Dave Mullally
Convex Computer Corp.

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From:	IN%"[email-masked]"  "Richard Bone" 31-OCT-1994 12:41:09.49
To:	[email-masked]
CC:	
Subj:	Re: CCL-Convergence in MOPAC

If I understand from your message correctly that you are experiencing
problems in converging geometry optimizations (irrespective of level
of theory) I refer you to my ERROR-correction notice, published in
QCPE bulletin, February 1994  (Vol. 14, No. 1, p.10).  I think that this
should fix you up.

Richard Bone

Richard G. A. Bone, PhD.
Computational Chemist
Terrapin Technologies, Inc.
South San Francisco
USA

E-mail  [email-masked]