Subject: DFT with high-spin iron complexes

From: "Christian Stadler" <[email-masked]>
Date: Mon, 29 Mar 1999 15:30:20 +0200

Dear CCLers

First of all thanks for all the answers regarding my problem with
"insufficiant memory ..." posted one week ago. (see: "technical 
problem with gaussian98 job") The problem really seems to be a "bug" 
in the G98 code regarding calculation of the amount of memory needed. 
I increased the %mem value only slightly and it worked. I did not try 
to decrease it as has been also suggested.

Now for the "new" problem. For almost three months now I've been
trying to perform DFT calculation on various iron complexes,
escpecially tris(acetylacetonato)iron(III) Fe(acac)3 with Gaussian 98.
I already tried B3LYP and SVWN with the LANL2DZ basis set - in one
case also a mixed LANL2DZ/6-31G(d) basis set. Unfortunately, the
mullikan and nbo population analyses yield rather strange results. All
calculations are performed on C1 symmetric molecules since we
discovered problems when C3 axes are present although the molecule
should have D3 symmetry.

One example:
Fe(acac)3 with SVWN/LANL2DZ gives a charge of 5.3 on Fe after the
first SCF and about -3.3 after the following SCFs according to NBO
analysis. At the same time there are no major changes in the
eigenvalues. However, some of them are pretty close and two of the 
alpha occ. eigenvalues are positive. In our opinion the result of 
the first SCF ist quite acceptable but the following SCFs seem to 
produce excited states. Is there a way to get further information 
about what's going on from the output files?

Would it be useful to introduce f-functions or to use a triple zeta
basis set? According to literature the chosen method should work but 
obviously it does not. :-(

Thanks and greetings

Christian Stadler
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Christian Stadler
c/o Prof. Dr. J. Daub
Institut fuer Organische Chemie
Universitaet Regensburg
93040 Regensburg
Germany

Phone: +49 941/943-4610
Fax:   +49 941/943-4984

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