From acp37@rs1.rrz.Uni-Koeln.DE Mon Nov 20 07:51:04 1995 Received: from rs1.rrz.Uni-Koeln.DE for acp37@rs1.rrz.Uni-Koeln.DE by www.ccl.net (8.6.10/950822.1) id HAA19008; Mon, 20 Nov 1995 07:42:17 -0500 Received: by rs1.rrz.Uni-Koeln.DE id AA73733 (5.67b/IDA-1.5 for CCL ); Mon, 20 Nov 1995 13:41:37 +0100 Date: Mon, 20 Nov 1995 13:41:37 +0100 (MET) From: "T. Koch" To: CCL Subject: How to measure stability Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII 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 /-----------------------------------------------------------------\ | Thorsten Koch | | Institut fuer Physikalische Chemie II der Universitaet zu Koeln | | Luxemburger Str. 116, 50939 Koeln, Germany | | acp37@rrz.uni-koeln.de | | Tel. +49 [0]221 470 4816 | \-----------------------------------------------------------------/