Subject: atomic symmetry in G94

From: [email-masked] (Georg Schreckenbach)
Date: Fri, 21 Nov 1997 09:22:04 -0700

Dear CCL,

I am trying to run a few atoms or ions (e.g., Fe_+) in
Gaussian 94, restricted open shell. My incentive is to
compare orbital energies as they come out of different
methods and / or basis sets.
   Now, when I run such an atom, the program turns off
symmetry. This would not bother me too much if the
subsequent SCF had not mixed up states. However,
it does so, and I do not get, for instance, 5 degenerate d
orbitals of the same energy. I tried to enforce some
symmetry by placing other nuclei into symmetric positions
far away but then I run into SCF convergence problems.

Any advice or tricks?

Best regards, Georg

--
==============================================================
Dr. Georg Schreckenbach           Tel:     (USA)-505-667 7605
Theoretical Chemistry T-12        FAX:     (USA)-505-665 3909
M.S. B268, Los Alamos National      E-mail:  [email-masked]
Laboratory, Los Alamos, New Mexico, 87545, USA
Internet:    http://www.t12.lanl.gov/~schrecke/
==============================================================

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From: "Dr. Alexei Arbouznikov" <[email-masked]>
Date: Fri, 21 Nov 1997 20:37:58 +0100 (MET)

Dear Georg,

	Unfortunately, if you use restricted Hartree-Fock within the
Gaussian program, you can not get the correct degeneracy of the open
shells, except for the simplest case of exactly half-filled open 
shells (try, e.g., Mn++ ion - d5 configuration, and you will obtain 5
degenerate d-orbitals). To get the correct degeneracy in some more
complicated configurations (non-half-filled one open shell or several open
shells, e.g., 3d and 4s with occupation numbers other than 1/2 for at
least one of them), you have to use GVB(0) option in the Gaussian, and
specify explicitely the vector coupling coefficients for the desired state
(the way to do it should be indicated in the G94 manual). Other solution
of this problem is using another ab initio programs with well-elaborated
ROHF techniques, such as, e.g., Monstergauss-92. 

	If you are interested in, please, ask some additional questions.

	Best regards,

	Dr. Alexei Arbouznikov

        Ecole Nationale Superieure de Chimie,
	Laboratoire de Materiaux Catalytiques et Catalyse en
	Chimie Organique, UMR 5618 CNRS-ENSCM - Prof. F.Fajula,
        8, rue de l'Ecole Normale
        34296 Montpellier, Cedex 5
        FRANCE

        Telephone: (33) 4-67-14-72-68
        Fax:   (33) 4-67-14-43-49
        E-mail: [email-masked]