Subject: Re: CCL:Use of AIM in Examining Transition States

From: Jamie Platts <Platts<<at>>Cardiff.ac.uk>
Date: Mon, 7 Jun 2004 15:42:42 +0100 (BST)

Hi Mark -

Good question, to which my answer would be yes, but only up to a point.
Most of Bader et al's ideas can be applied to any electron distribution,
whether at a stationary point or not. Thus, it is possible to define a
basin which obeys the zero-flux condition, and associated interatomic
surfaces at any point on the PES. Having done this, one can generate the
usual atomic charges, multipoles etc. Critical points are similar, and
are generally conserved at small changes away from equilbrium.

There are two main caveats to this statement. Firstly, calculation of
an atomic energy in Bader's scheme is only valid at a stationary point on
the PES, since it assumes there are no (Hellman-Feynman) forces on nuclei.
Clearly, this is fine for a true TS or other saddle point.

Second, the identification of an atomic interaction line with associated
(3,-1) critical point with a bond is only strictly valid at equilibrium.
So at a TS, the presence of a (3,-1) cp is not enough to state that two
atoms are bonded, but only that they're interacting.

An example of applying AIM to transition states is our old paper:
J. Phys. Chem., 1996, 100, 13455. Please note that I'm not claiming this
to be the first or the best, just the one for which I have the reference
to hand .

Hope this helps,

Jamie

----------------------------------------------------------
  Jamie Platts
  Dept. of Chemistry  		Phone: +44 (0) 2920 874950
  Cardiff University 	 	Email: platts<<at>>cf.ac.uk
  P.O. Box 912 			FAX:   +44 (0) 2920 874030
  Cardiff CF10 3TB 		www.cf.ac.uk/chemy

> Can AIM be used to evaluate bonding in a transition state structure?
> After reading Bader's web site, he often refers to equilibrium
> structures.  Yet it seems that there is no apparent prohibition against
> employing AIM to studying transition states.  Since AIM is based on a
> physical observable and a TS is not a physical observable is it still
> valid to apply AIM analysis to a transition state?
>
> Thanks!
>
> Mark
> ************************************************
> Dr. Mark A. Zottola
> Army Research Laboratory
> Aberdeen Proving Grounds
> PB #134 939-I Beards Hill Road
> Aberdeen, MD 21001
> Voice: 410 278 7250  FAX: 410 297 9521
> Email:  mzottola<<at>>arl.army.mil
>
>
>

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From: "E.L. Willighagen" <egonw<<at>>sci.kun.nl>
Date: Mon, 7 Jun 2004 11:23:21 +0200

On Saturday 05 June 2004 14:20, hinsen<<at>>cnrs-orleans.fr wrote:
> On 04.06.2004, at 13:46, jle<<at>>theworld.com wrote:
> Beyond all the more or less objective comparisons, there is one aspect
> that is rarely mentioned: you should pick a language that suits your
> way of working and thinking. Just like some people prefer geometry and
> others algebra for attacking the same problem, some programmers get
> better results with one langugae and others with another one. 

That's indeed an important point... I've spent too many hours finding bugs in 
C/C++ code dealing with memory issues, which sometimes where even caused by 
compiler differences... While this is likely no problem when working a lot in 
C++, in Java I never had such problems...

Egon

- -- 
egonw<<at>>sci.kun.nl
PhD on Molecular Representation in Chemometrics
Nijmegen University
http://www.cac.sci.kun.nl/people/egonw/
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