Subject: How to measure stability

From: "T. Koch" <[email-masked]>
Date: Mon, 20 Nov 1995 13:41:37 +0100 (MET)

Dear netters,

I have a question which should be of considerable interest for 
computational chemists. The question is: How do I measure computationally 
the stability of organic molecules?
  I study some molecules which presumably have not yet been prepared. And I 
would like to know if these molecules have a chance to exist. What I did 
so far is the most simple and obvios method: I compared the absolute 
electronic energy with the same quantity on a known and more or less 
stable isomer. But from the results I got I think that this is only a 
crude approximation on a "measure" of stability and reactivity.
  What I didn't examine yet but could be quite sensible (I think) is doing 
a CI or MCSCF calculation and looking at the energy gap between the 
frontier orbitals and comparing it to known isomers.
  Another way could be an examination of the computed IR-spectrum. Are 
there very low frequencies (shallow dips in the potential engergy 
surface) which could lead to "new" molecules?
  Is there a way to determine "centers of reactivity" ?
  
  Has someone any ideas about this topic?

  I will summarize it to the list, if I get any responses ;)

Bye, Thorsten

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|                        Thorsten Koch                            |
| Institut fuer Physikalische Chemie II der Universitaet zu Koeln |
|           Luxemburger Str. 116, 50939 Koeln, Germany            |
|                    [email-masked]                       |
|                   Tel. +49 [0]221 470 4816                      |
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