Subject: SUMMARY: error/accuracy determinations for S.E. application

From: "Soar, Terri Jacqueline - SOATJ001" <[email-masked]>
Date: Mon, 11 Jan 1999 15:32:56 +1030

Hi all.

Thanks to those 3 people who replied to 
my plea for any ideas/help (these are listed below).
(Thanks Andrew, I have read your paper)

I have a few other resources to check out before
I decide what will be the best way to go on
this topic. 

If there are any other delayed thoughts about this 
problem that may be of use to me, it's not too late
to post them!

Regards,
Terri
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Ms. Terri Soar, PhD student,
Ian Wark Research Institute,     tel: +61 8 8302 3706
University of South Australia,    fax: +61 8 8302 3683
The Levels Campus,	
Mawson Lakes, S.A. 5095, AUSTRALIA
email: [email-masked] <mailto:[email-masked]> 
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REPLIES TO MY QUERY (as shown last on this list):
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take a look at:
Gale, J. D., Rohl, A. L., Watling, H. R., Parkinson, G. M., Theoretical
Investigation of the Nature of Aluminum-Containing Species Present in Alkaline
Solution, The Journal of Physical Chemistry B; 1998; 102(50); 10372-10382.
Andrew :-)
Andrew Rohl [[email-masked]]

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Well, I think the state of the art (I'm a full time follower but only a part
time practicioner (sp?)) for systems with no direct experimental counterpart is
to choose your simples system (say a dimer) and model it with increasingly
sofisticated ab inito methods until the answer doesn't change any more. If this
is similar to your calculated results then the semi empirical results are
valid. By the way, heats of formation themselves are somewhat meaningless.
Relative heats of formation mean more (such as delta Hf between 2 monomers and
a dimer, or a solvated dimer vs an unsolvated dimer.
Good luck. I wish there was a simple solution.  I would be interested in
reading your other responses.

Kimberley Cousins
Associate Professor of Chemistry
California State University, San Bernardino
5500 University Parkway
San Bernardino, CA  92407
(909)880-5391

[email-masked] <mailto:[email-masked]> 
http://chem.csusb.edu/~kcousins <http://chem.csusb.edu/~kcousins> 

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Just a quick note to say that I was involved in something like this previously,
although the system/species were different.  Si/AL(O)x(OH)y clusters relating
to zeolites but we have published the results. Here I think we discussed some
thoughts relating to the accuracy and how we might be able to extrapolate the
results to chemically related systems regarding the formation of Lowensteins
Rule in zeolites.
Hopefully it might be of some help 
C.R.A. Catlow, A.R. George & C.M. Freeman, "Ab-initio and Molecular Mechanics
Studies of Aluminosilicate Fragments and the Origin of Lowenstein's Rule.",
Chem. Comm., 1311-1312, (1996).
I've also cc this to Prof. Richard Catlow who is still very active in the area
but I feel does not have time to follow the group.
Hope this helps 
Cheers
Ashley
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Ashley George,      Phone : 0118-977-3133
Cerebrus                Direct  : 0118-989-9317
613 Reading Rd.   Fax     :  0118-989-9300
Winnersh, Berks   Email  : [email-masked]
<mailto:[email-masked]> 
RG41 5UA. UK    URL   : http://www.cerebrus.ltd.uk <http://www.cerebrus.ltd.uk>

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My original query was:

Hi CCLers.
I'm after some ideas, pointers or even just people's thoughts as to the topic
of calculating the accuracy of calculations.
This is the situation...For my PhD in physical and inorganic chemistry about
one quarter of my work has involved applying computational chemistry. The
computational chemistry work has focused on a range of aluminium-oxyhydroxide
species (monomer, dimer, trimer, tetramer and some polymers) that may exist in
aging caustic aluminate solutions where crystalline Al(OH)3, i.e. gibbsite,
finally precipitates out. 
We are using MOPAC93 with AM1 (i.e. semi-empirical quantum mechanical
methodology) and also with and without COSMO (to include solvent effects) to
perform geometry optimisations and SADDLE calculations on these species where
our main interest is the stability and also the relative energetics of the
species (wrt to heats of formation and reaction and also Gibbs free energy of
formation and reaction) to indicate what species are more likely to exist in
these solutions and participate in reactions possibly leading to gibbsite
formation.
So, how would I go about estimating errors and determining accuracy for this
work (keeping in mind that many of the solution species we've modelled cannot
be measured experimentally (i.e. heats of formation))? 
As I've said above, I'm after any answers to this question in addition to
people's thoughts as to what may be expected in the way of accuracy
determinations for this type of work.
Thanks in advance and, of course, a summary will be produced.
Terri