Subject: CCL:How to define HOMO-LUMO gap in open shell system ?

From: Ricardo Oliveira <organicjewellery-.at.-yahoo.com>
Date: Mon, 4 Jul 2005 05:45:36 -0700 (PDT)

Dear all,

 I have noticed that some excitation energies , in
closed shell systems, have energies similar to the
HOMO-LUMO gap.

 Considering that the term 'HOMO-LUMO gap' is not very
appropriate for open shell systems, how can we do a
rough estimate of the excitation energies in this
case?
Shall they be somewhat similar to the homo-somo(singly
occupied orbital) gap?
Can the gaps mentioned by Ding Xunlei,on his CCL
communication, have any meaning at all?

Thanks

Ricardo O Esplugas
Dept of Chemistry
Sussex University
UK

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