Subject: summary iron calculation

From: [email-masked] (Dr.Pierre Acklin)
Date: Mon, 17 Oct 94 16:24:29 +0100

Dear Netters,

	two weeks after the posting of my questions about calculating
iron complexes with ab initio or semiempirical methods to the list,
I'll summarise the answers I've got until now after the repetition of 
my original query.

	Many thanks to all of you who have replied.

>	I am trying to model iron complexes with round about 30 
> heavy atoms. Introducing special angular and torsional constraints
> into amber force field calculation in MacroModel leads to good 
> and reproducable geometry predictions. 
>	Geometry predictions are ok as they allow to discriminate 
> between molecules which can form chelate complexes and those, which 
> can't. Nevertheless it would be very helpful for the project, if 
> some kind of energy or stability predictions would be possible.
> This makes me ask you the following questions:

> Is it possible to treat iron complexes with more than 30 heavy
> atoms in an ab initio program like Gaussian in a reasonable time
> on a SGI workstation?

> Are there any basis sets and references therefore available to
> handel iron in Gaussian92 or DFT on a better level than sto-3g?

> How good are results of semi empirical calculations form Ampac 
> or Zindo in terrms of energy and geometry?

> I'll be glad to summarise the responses for the list.

*******************************************************************

Dear Dr. Acklin,

concerning your CCL-questions about iron complexes, we can offer you
the possibility to do your calculations on our
CRAY C90 supercomputer here at the University of Stuttgart, Germany.
The machine has 4 CPU's, 8 GBytes of main memory and much more than
100 GBytes of local disk space available.
Of course this is not for free, so we charge some small
amount per cpu-hour ( DM 300,- without service, DM 500,- including
service, doing batch-calculations with normal priority) for industrial
customers.

Best regards,
Heinz Poehlmann

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Dear Pierre,

it is always a question of time and precision...and symmetry of course!
My experience with ab initio calculations in this field is that they have
to be carried out at least at the MP2-level of theory (for first row
transition metals, heavier give reasonable geometries already on the HF
level!). MP2 usually increases computational time and hard disc require-
ment. See recent papers by Gernot Frenking for ab initio calculations
involving transition metals.
I got the impression that DFT makes it slightly easier to handle larger
TM complexes since electron correlation is always included while 
computational efford is comparable to HF calculations. There is a recent
review by Tom Ziegler covering this topic:
Tom Ziegler, Chem. Rev. 1991,91,651-657
I currently carry out DFT calculations on large metallocenes and the
results come in...
I have heard a lot about ZINDO, also on Iron complexes. Results looked
good, though I cannot tell anything about it. Look for papers by
Reinhold's group in (Leipzig, Halle, Magdeburg; sorry don't know 
exactly) and the original papers of course...
Finally there are still Extended Hueckel calculations. Hoffmann in 
Munich is a good reference for these....

Hope this helps,

John Lohrenz

-----------
John Lohrenz
Dept. of Chemistry
Univerity of Calgary
email: [email-masked]

***********************************************************************

Dear Pierre

I have been doing calculations on organomettallic iron compounds of 
about 20 atoms (1 iron, 9-10 carbons, 2 oxygens, rest H). I was using 
STO-3G for geometry optimizations (there are a few problems with this 
of course) and something better for single points.

> This makes me ask you the following questions:
> 
> Is it possible to treat iron complexes with more than 30 heavy
> atoms in an ab initio program like Gaussian in a reasonable time
> on a SGI workstation?

If you're interested in single point, this should be no problem, 
depending on how much correlation you want to include. In GAMESS a 
single point calculation (78 basis functions) took about 12 minutes 
on a SGI Indego 2 (100MHx R4000). You may want to use Effective Core 
Potentials (ECP's) in your system.
> 
> Are there any basis sets and references therefore available to
> handel iron in Gaussian92 or DFT on a better level than sto-3g?

Yes you can check the papers by Marynick et al or use the predifined 
ones in the package.

D. S. Marynick et al, Organometallics, 1991, 10, 2816-2823 and refs therin.
> 
> How good are results of semi empirical calculations form Ampac 
> or Zindo in terrms of energy and geometry?

I tried ZINDO calculation on my systems, but got very strange 
structures forming (eg carbonyls were pulled off the metal and 
incorporated into a alkyl chain, forming a small ring system). I have 
a feeling it works better for coordination complexes, but no 
experience myself. It should be remembered that ZINDO's primary aim 
was the description of electronic transitions in Metal-Ligand systems 
(See Michael Zerner's work on Porphrins etc).

No experience with Ampac. Spartan, from Wavefunction inc is busy 
working on semi empirical parms for 1st row TM's.

Good Luck

Oliver
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**************************************************************************

 Dear Pierre,
    A good basis for iron, and other first transition series, is Wachter's
 as implemented in HONDO8.
  Yes you can run upto 30 atoms, SCF direct, using Gaussian, hopefully in
 less than 12 hours.
  No, you cannot use AMPAC for iron but I believe SAM1 has recently been
 parameterized and other semi-empirical codes include ZINDO (from BIOSYM) or
 MNDO-d (from W. Thiel, Zurich),
   Good luck,
      John Waite ([email-masked])
 PS I would be interested in other transition metal bases.

********************************************************************

Hi!

I have been doing computations on  iron porphyrins with ADF, the
Amsterdam Density Functional program, on an INDIGO R4000  from SGI.
The performance is  pretty good and you get all the benefits
of DFT computations. Namely, almost MP2  quality for energetics.

Regarding DFT  in G92, I had a bit of a bad experience since the
guess for the density is based on a semiempirical HF computation,
a very bad guess for my high  spin system. Moreover, I could not
converge on  ROHF and use the density for G92/DFT.  I also had
to use the  finegrid as default, otherwise, the numerical integration
scheme would complaint.  Hence, I left DFT/G92 behind, but I remind
you  that some  of these  problems (i.e. the numerical  integration bit)
have been addressed through upgrades.

I am very  happy with ADF. It  has  recently been  upgraded to
give thermochemistry data and  many  of the features that  you
find  in G92.  Nevertheless, ADF still has  some way to go before
it can compete with G92, particularly regarding the variety of
functionals that you  get with G92.

Regarding  basis sets, ADF  comes with its own  suite  of
basis sets since it uses STO.  For G92 and similar programs
you are better off using ECP's. Check out the work by CUNDARI who
has done HF like computations with  ECP in several  transition metal
complexes. I give you  references below to some ECP's that CUNDARI
has used successfully  in  studying the energetics and geometries
of several tm complexes.

Finally,  I run  with  C4v  or D4h symmetry using a triple Z basis
set on the Fe and double Z with  polarization  on the light atoms.
Single point computations on a single user  R4000 SGI and ADF v. 1.0
take around 4-5 hrs. The newest version implements the DIIS algorithm
so convergence is much faster. I think this will make a big difference.

**************     

The following references should provide you with very recent ECP's for
most of the periodic table. The comments I have heard from those who
have used them are rather favorable (comments limited to energetics and
geometries, but recent work on spectroscopy by Garmer and Krauss is rather
impressive):

	Stevens et. al. J. Chem.Phys. 81 (12), Pt. II, 1984
	First and Second Row atoms

	Stevens et. al. Can. J. Chem. 70, 612, (1992)
	Third through Fifth row atoms. Some typos are known:

	Table 2: In RECP for second Vp-f component:
			-129.87594 should read -129.78594
	Table 4: Basis for Fe
			Cp term for 1sp should be -0.007940, not -0.07940
			asp term for 4sp should be 0.0410, not 0.410
	Table 7: Result for Be
			Eval with core a should read -1.01214, not -0.01214

	Cundari and Stevens J. Chem. Phys. 98 (7) 1993
	Lanthanides

I hope this is useful. These papers also discuss the variety of methods
available to generate ECP's, relativistic effects and references to ECP's
for DFT computations.

Good Luck
Gustavo A. Mercier, Jr.
[email-masked]

***********************************************************************

Dear Dr. Acklin,

  As you are aware (from your message)  our AMPAC program includes
the new SAM1 Hamiltonian which can treat iron systems.  We are
quite pleased with the results.  If you would like to provide a
test molecule or two, we would be happy to run it for you.  (A
set of cartesian coordinates would be best.)

  On another note, up until recently, your company owned a license to
AMPAC.  Heinrich Karfunkel elected to allow that license to lapse
because he disagreed with our licensing scheme.  Your New York
research site still owns a license, so we would be happy to provide you
with a second license at our very reduced rate if you find that
you need the program in Basel.

  Andy Holder

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                    DR. ANDREW HOLDER
                   President, Semichem

Semichem, Inc.            ||  Internet Addr: [email-masked]
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Shawnee, KS,  66216       ||  FAX Number:    (913) 268-3445
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==========================================
Dr.Pierre Acklin
CIBA-GEIGY AG
K-136.P.13
CH-4002 Basel         [email-masked]
++41 61 696 23 62
++41 61 696 23 75
==========================================