Re: CCL:coordination compounds in MM3

 	Dear Jeny,
 
 I want carry out some calculation on a metal-porphyrin coordination
 compound using MM3 force field. From MM3 manual, there should be two
 modification (1,3-electron pair repulsion and bending parameter
 adjustment). However, I didn't find what special commands I should use to
 indicate those coordinate bonds (eg. in conjugated systems we have to
 specify those pi atoms). Would anyone who is familiar with MM3 tell me
 what kind of special treatment I should apply to the coordination
 compound?
It depends on which implementation of MM3 you're using, they all differ. If it's the original MM3 program from Allinger, then the atom type determines if it is a coordination center. If it is, any bond to it counts as a coordination bond.
In addition to the bending parameters, for optimal results you should also specifically parameterize the bond lengths, but if you're using MM3(96) (or later), I believe you'll get rough guesses
from the parameter estimator, that will serve for quick-and-dirty 
 calculations.
You didn't write your name, but I think I recognize the email address, haven't we been in contact before? 
 	Best regards,
 	Per-Ola Norrby
 --
 Per-Ola Norrby, Assoc. Professor, http://organisk.kemi.dtu.dk/PON/
 Technical University of Denmark, Department of Chemistry
 Building 201, Kemitorvet, DK-2800 Kgs. Lyngby, Denmark
 Email: pon [] kemi.dtu.dk  tel +45-45252123,  fax +45-45933968