Subject: ab-initio calculation of UV/VIS-spectra

From: Oliver Kohlbacher <[email-masked]>
Date: Thu, 13 Nov 1997 16:36:35 +0100

Dear CLLers,

what possibilities do exist to predict UV/VIS spectra of
aromatic compounds? To my understanding, it should be possible
to predict them from the orbital energies obtained by a
CI calculation. How difficult is this task? 
And how to get intensities?

Thanks for any advice,
  Oliver

-- 
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 Oliver Kohlbacher   ([email-masked])
 Max-Planck-Institut fuer Informatik, Im Stadtwald, 66121 Saarbruecken
 Tel.: 0681-9325-505 Fax: 0681-9325-199

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From: Charles & <[email-masked]>
Date: Thu, 13 Nov 1997 13:34:05 -0500

> And how to get intensities?
	The easiest way to do this is to use ZINDO or MOPAC.
The ZINDO package has been parameterized to reproduce UV/VIS
spectra for organic and transition metal compounds using
a singles CI.  I think you can purchase this through Hypercube.
It is fairly easy.  Intensities are harder to model, but 
ZINDO maybe provide reasonable results.

	Ab initio spectra are much harder to obtain because of the
computational requirements for accutate calculations.  I would
think that you could obtain crude UV/VIS spectra using Gaussian
with the CASSCF+MP2 option, but this is hard to run on anything
but relatively small systems (i.e. no more than say 10 pi orbitals).
The Guassian CIS option may work, but I doubt it will be better than ZINDO.
You might also try ACES, which using a type of coupled cluster + 
equations of motion approach, but, again, this will require a lot
of disk space and memory. 

	Chuck Martin

-- 
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Dr. Charles H. Martin
Quantum Theory Project
362 Williamson Hall
PO Box 118435
University of Florida
Gainesville, Florida  32611-8435

Fax: (352) 392-8722
Email: [email-masked]
Web:   www.cat.syr.edu/~cmartin/hv
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