CHARMM forcefield was developed for representing protein & organic molecules.

and also, Hem containes Ferrous(Fe 2+) as a cofactor.

This makes the system not to be treated by Force Field(rather Classical Mechanics)

shouldn't properties of transition metals calculated by Quantum Mechanics?

from charmm website, I found link below concerning Heme parameters.

http://www.charmm.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=31530

http://www.charmm.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=33417

one more, below a group made parameters by QM calculations

https://www.researchgate.net/publication/8445805_Classical_Force_Field_Parameters_for_the_Heme_Prosthetic_Group_of_Cytochrome_c

hope this might help you!

Article Classical force field parameters for the heme prosthetic gro...

Hi,

You can download the last version of the c36 forcefield from MackerellLab :

http://mackerell.umaryland.edu/download.php?filename=CHARMM_ff_params_files/toppar_c36_aug15.tgz

In the stream/prot subdirectory there is a file containing HEME parameters and topology : toppar_all36_prot_heme.str

Regards,

F Hédin

Florent, Like I said I know about this but I was wondering if the same is available for oxidized state? Also It doesn't have the patches for CYS linkage for c type heme. Thanks though.

Atanu

Check out this article and especially pay attention to the supplementary material

Main Article

http://www.cell.com/biophysj/abstract/S0006-3495%2808%2982003-6?cc=y=

Suppl. Mat.

http://www.cell.com/biophysj/supplemental/S0006-3495%2808%2982003-6

The patches can be found in CHARMM but there are also patches available from

http://link.springer.com/article/10.1007/s00214-013-1370-8

In their supplement, but you'll need to be an authorized user or pay.  This last one is for the HEME C type in bc1 (complex III) but it has the same topology as HEME C found in cytochrome C (except possibly the charges).  I'm not certain about states other than reduced for heme B.

 Thanks Daniel. Those were really helpful.