Subject: Re: CCL:porphyrin

From: Mikael Johansson <mpjohans^at^pcu.helsinki.fi>
Date: Tue, 18 Jan 2005 21:10:59 +0200 (EET)

Hello Christophe and All!

On Tue, 18 Jan 2005, Christophe Biot wrote:

> I would like to perform an analysis of the geometrical and electronic 
> structure of some iron-porphyrin derivatives.
>
> Could someone advise me about the method of choice (DFT, HF, MP2...) 
> for such kind of calculation?
> And also about the basis set (Lanl2dz, LanL2dm, SDD, ...) to use?

DFT is the method of choice here. HF is totally useless (except for 
producing amusing results :-). MP2 is not very good either, being based on 
the HF reference wave function. Also, the HOMO-LUMO gap in these systems 
is often also quite small.

The basis set required depends on the property in question. A good general 
starting point would be a polarised double-zeta for all except iron, which 
really could use a polarised triple zeta basis. My experience is mostly 
with the Ahlrichs bases SVP, TZVP...

I've done some work on the properties of iron porphyrins [1-3]. In [3] the 
performance of DFT was compared to the approximate second order coupled 
cluster methods, CC2. DFT was better.

Have a nice day,
     Mikael J.
     http://www.helsinki.fi/~mpjohans/

[1] M.P. Johansson, M.R.A. Blomberg, D. Sundholm, M. Wikström, "Change in
     electron and spin density upon electron transfer to haem", Biochim.
     Biophys. Acta - Bioenergetics 1553 (2002) 183-187.
[2] M.P. Johansson, D. Sundholm, G. Gerfen, M. Wikström, "The Spin
     Distribution in Low-Spin Iron Porphyrins", J. Am. Chem. Soc. 124
     (2002) 11771-11780.
[3] M.P. Johansson, D. Sundholm, "Spin and charge distribution in iron
     porphyrin models: A coupled cluster and density-functional study", J.
     Chem. Phys. 120 (2004) 3229-3236.