Subject: degenerate representations and quantum packages
From: <makowskm_at_chemia.uj.edu.pl>
To: chemistry_at_ccl.net
Date: Wed, 16 Jul 2003 08:12:42 +0200 (CEST)

As far as I know symmetry groups with degenerate representations are not
treated exactly by any standard quantum chemiacla package. Instead they
work in the largest abelian subgroup which will be in your case D2. That
is why you may obtain symmetry-broken state.
Yours,

 --
Marcin Makowski
Ph.D. student in Theoretical Chemistry,
Jagellonian University

> Dear CCL-ers,
>
> Recently I encountered the following problem. When calculating (by
> Gaussian 98) excited states of a molecule optimized with imposed D2d
> symmetry constrain I got the strange features of the calculated excited
> states. Namely, I got different calculated energies and (sometimes)
> quite different oscillator strength for degenerate transitions.
> Nevertheless, Gaussian denotes excited states being degenerate and
> having E-symmetry. Can anybody explain me why is it so?
>
> Best regards,
> Igor.
>
>
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From [email-masked] Mon Jul 21 15:34:15 2003
Date: Mon, 21 Jul 2003 15:31:04 -0400
To: chemistry$at$ccl.net
From: "William F. Polik" <polik$at$hope.edu>
Subject: WebMO 3.3: WWW-based interface to Gaussian, MOPAC, and GAMESS

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From [email-masked] Mon Jul 21 11:45:48 2003
Date: Mon, 21 Jul 2003 16:45:47 +0100 (BST)
From: Jamie Platts <Platts^at^Cardiff.ac.uk>
To: chemistry^at^ccl.net
Subject: CAS-SCF active space

  Hi Folks - I wonder if I can ask your advice on selecting active spaces
for CAS-SCF calculations. I have a system which wants to form a broken-
symmetry singlet UHF wavefunction, rather than the expected RHF one.
The natural orbitals from this (152 e) UHF wavefunction look like:

                     71        72        73        74        75
EIGENVALUES --     1.97076   1.95176   1.94478   1.78912   1.46209

                     76        77        78        79        80
EIGENVALUES --     1.22142   0.77858   0.53791   0.21088   0.05522

Can I safely ignore everything up to 73, and use a (6,6) active space
made up of 74 to 79? Or is 1.95/0.05 too big to ignore?

  Many thanks in advance,

  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