Subject: Ab inito/DFT calculations on non-unity multiplicity metal complexes

From: "Sheldon M. Williams" <[email-masked]>
Date: Thu, 13 Mar 2003 11:42:42 -0600 (CST)

Hello,

I have been having problems with SCF convergence and running out of memory
trying to perform ab inito geometry optimization calculations on Cu(II)
and Fe(III) ion complexes with crown ethers. I run MMFF conformational
searches with the ion constrained near the center of the crown ether ring
to get close to the global minimum, as I get poor configurations with low
level calculations if I do not contrain these metal ions. I then do a PM3
geometry
optimization, if possible. After this I have attempted both ROHF/ and
UOHF/3-21G*, 6-31G*, and LACVP* geometry optimizations with SCF cycles set
to up to 5000, but the calculation always runs out of memory. I'm
performing the calculations with Spartan PC 2002 on a 2.0GHz P4 with 1.0GB
of SDRAM. Trying to perform a DFT calculation directly from the MMFF or
semi-emperical geometry has worse SCF convergence and memory problems.

It appears to be a problem of the multiplicities of these complexes as
Ag(I) and Cu(I) work. Almost all papers on ab initio or DFT calculations
on transition metal-ligand complexes use the oxidation state with
singlet multiplicity. I haven't gotten any useful info from support at
wavefunction. I would be grateful if you could suggest what the
problem might be or direct me somewhere I could find help?

Thank you for your time and attention,

Sheldon M. Williams
Ph.D. Candidate, Analytical Chemistry
Jennifer Brodbelt Lab
Chem & Biochem Department
1 University Station A5300
University of Texas at Austin
Austin, TX 78712
Phone:(512)471-0041
FAX: (512)471-8696
E-mail: [email-masked]