Subject: mn complexes

From: michael nolan <[email-masked]>
Date: Wed, 30 Apr 1997 12:55:12 +0100 (BST)

Dear CCL

HELP!

I have a really bad problem and I cannot do anything about it.
Here it is:
I am trying to run ab-initio calculations on Mn(CO)3 and Cr(CO)3, using
GAMESS-UK.
I have tried the following methods (I also give if ti was succesful or
not):

1) RHF/3-21G (3-21G on all atoms)
for Mn(CO)3 this is successful, for Cr(CO)3 I get excessive number of
iterations and an oscillation of the energy.
geometry input: Caetesian coordinates, i.e
geometry angstroms
0.000 0.000 0.000 metal
1.800 0.000 0.000 c
 ....
 ....
3.000 0.000 0.000 o
 ...
 ...

runtype: OPTXYZ

2) RHF, 6-21G on C and O, 3-21G on Mn.
for Mn(CO)3, this is successful

3) RHF with minimal basis ECP on all atoms for Mn(CO)3 and Cr(CO)3.
This gives a ludicrously low energy (about -70a.u.), oscillations in the
energy and excessive number of iterations
I have inputted a z-matrix, cartesian coordinates from X-ray diffraction
studies (using both OPTXYZ keyword and the cartesian coordinates to
z-matrix conversion) and the idealised geometry above  and I get the same
result with them all - excessive number of iterations etc..

4) RHF as above, but ECP-double zeta (ECPDZ) on all atoms
same result

5) RHF, min. basis ECP and ECPDZ on Mn, 3-21G and 6-31G on C and O
see number 4.

I assume the fact that Mn(CO)3 is positively charged has nothing to do
with it (it is a closed shell).
I know that 3-21G and 6-31G are not good for transition metals, yet I got
reasonable results using these (MOs and charge distribution).

Does anyone have any ideas for how I can use ECPs (we are limited to about
1.2GB) or anything else to get these calculations to run (we do not yet
have DFT).
As an aside, I keep getting an error message when converting from
cartesian coordinates to z-matrix. Has anyone else had this?

sorry for bothering you and
thank you in advance

Michael Nolan

Der Kobold hat gesprochen
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Michael Nolan (nearly BSc.)		Dublin City University (quantum chem.)
41 Woodview				Chemistry + German Year 4
Lucan
Co. Dublin
Ireland / Republic of Ireland / ROI / Eire

Email: [email-masked]
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