Heme charges

From: Emad Tajkhorshid <emad/at/ks.uiuc.edu>
Subject: Heme charges
Date: Tue, 5 Aug 2003 11:52:27 -0500 (CDT)

Hi,
 We just optimized the geometry of a porphyrin ring using DFT and
 calculated ESP charges for the molecule. The iron carries a significant
 amoount of positive charge according to population analyses done on the
 system (it is formally 2+), but the ESP charge for it is negative! The
 iron atom is completely burried inside the molecule, and that may be one
 reason of getting this strange result. Has anybody else had similar
 problems? Any comments, references, or suggestions are
 appreciated.
 Thanx a lot.
 Emad
 ------------------
 Emad Tajkhorshid, Ph.D.        http://www.ks.uiuc.edu/~emad
 Assistant Director of Research
 NIH Resource for Macromolecular Modeling and Bioinformatics
 Theoretical and Computational Biophysics Group
 Beckman Institute, 405 N. Mathews,  Urbana,  IL 61801,  USA
 Tel:(217)244-4361 Fax:(217)244-6078 Email: emad/at/ks.uiuc.edu