Re: CCL:porphyrin

[Mikael Johansson <mpjohans^at^pcu.helsinki.fi>]

 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.