Subject: Re: CCL:AM1/PM3/MNDO parameters for Fe and Ni?

From: "Andy Holder" <[email-masked]>
Date: Fri, 13 Dec 1996 10:11:30 -0600

Netters,

In reply to:

> A colleague of mine is looking for semiempirical parameters (AM1,PM3 
> and/or MNDO) for Fe and Ni. I already searched the CCL archives but 
> the only thing I found were similar questions... no answers. 

I have seen this question asked a number of times (and with increasing 
frequency) in the last months.  I wanted to take a moment to explain why there 
are no good answers to this exact question and what the alternatives are.

The currently popular Dewar-style methods (MNDO, AM1, and PM3) are not suited 
in their original incarnations for treating transition metals.  This is simply 
because the original formulation of these models did NOT contain d-orbitals.  
The main group elements can be handled because the valence shells are only s 
and p.   (Note that Zn, Cd, and Hg are also treatable because they have closed 
d-shells and can be treated as basic s2 elements.)

(It is correct that d-functions are needed for proper treatment of these 
elements at the ab initio level (and perhaps the semiempirical as well!), but 
we are focusing on actual orbitals here, not polarization functions.  There 
has been quite a lively debate in the literature about the actual role of 
these functions in hypervalent main group elements.  This focuses on whether 
they act as mere polarization functions or actually particiapte in bonding in 
keeping with an sp3d2 hybridization idea.) 

Now, how do we get around this?  There are two basic schools of thought:

1.  Extend the multipole expansion (ME, the technique used to compute two-
electrons repulsion integrals (TERIs)) to d-orbitals.  This has advantages, in 
that it is very fast and we can take advantage of previous parameters.  This 
was the approach pioneered by Walter Thiel and coming to fruition in the so-
called MNDO/d method (available now in Unichem and soon in AMPAC and other 
places).  This treatment was extended to PM3 and I believe AM1 by some people 
at Wavefunction (found in Spartan).  It should be noted with some caution that 
these elements were parameterized with reference ONLY to X-ray geometries of 
closed-shell molecules.  Traditionally, gas-phase heats of formation, 
ionization potentials, dipole moments, and geometries are used to give a 
balanced picture of a variety of properties, resulting in a general method.

MNDO/d References:
Thiel, W.; Voityuk, A. A. Theor. Chim. Acta  1992, 81,  391.
Thiel, W.; Voityuk, A. A. Intl. J. Quant. Chem.  1993, 44,  807.
Thiel, W.; Voityuk, A. A. THEOCHEM  1994, 313,  141.
Thiel, W.; Voityuk, A. A. J. Phys. Chem.  1996, 100,  616.
Thiel, W. Adv. Chem. Phys.  1996, 93,  703.

2.  Scrap the ME and use something different.  This was the approach taken in 
the Dewar group and followed up in my group with SAM1 and (hopefully) its 
successors.  Here we used a simplified set of Gaussian orbitals that are 
semiempirically scaled for computing TERIs.  This gives a different method of 
computing these quantities, one that we hope is better.  It should also be 
noted that this approach requires a COMPLETE reparameterization of the 
methods.  This is both good and bad.  "Bad" because it is a great deal of 
work, but "good" because the older parameters were derived in times of much 
more limited computer resources. We can now afford to do MUCH more extensive 
searches than previously and use larger molecules and basis sets of systems 
for parameterization than ever before!  This is SAM1 and it is currently found 
in our AMPAC.  

SAM1 References:
Dewar, M. J. S.; Jie, C.; Yu, G. Tetrahedron 1993, 23, 5003.
Holder, A. J.; Dennington, R. D.; Jie, C. Tetrahedron 1994, 50, 627.
Holder, A. J.; Evleth, E. M. in Modeling the Hydrogen Bond; Smith, D. A.;  
    American Chemical Society, Washington, DC,1994; pp 113.

Currently work is going on in several places (including here and in Professor 
Thiel's lab) to complete these methods for more of the periodic table.  Stay 
tuned.

I should also note that ZINDO (M. Zerner, U. of Florida) has been available 
for quite some time and handles these elements, but has some constraints.  
Also, one can always do ab initio (standard basis sets exist) or DFT.

Hope that this helps.

Regards, Andy Holder

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UUUU  UUU MMM   MMKK KKKK   CCCC   |           ANDREW J. HOLDER
 UU    U   MM   MMK   K    CC  CC  | Assoc. Prof. of Comp./Org. Chemistry
 UU    U   MMM M MK KK    CCC      |          Dept. of Chemistry
 UU    U   M MM  MK   KK   CC  CC  |  University of Missouri-Kansas City
  UUUUU   MMM M MMKK   KK   CCCC   |         Kansas City, MO  64110
                        KK         |          [email-masked]
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