[gmx-users] CHelpG charges on Fe-PPIX

Valentin Gogonea v.gogonea at csuohio.edu
Wed Jan 22 13:29:13 CET 2003

Dear CCLers and GMX users,

A couple of months ago I asked a question about what van der Waals 
radius should be used for Fe(2+) to obtain CHelpG charges (to be used 
with OPLS parameters). I got few replies and consequently, following 
the suggestions from the list I tried few exploratory calculations on 
Fe(2+)-porphyrin IX (without axial ligands). I am listing here the 
results obtained for different van der Waals radii in the range of 

CHelpG charges for Fe(2+)-PPIX
Total Charge=0, Multip=5

Radius-Fe(A)     Charge(au)
1.0		      4.226756
1.2		      3.069658
1.5		      0.943646
1.7		    -0.342193
2.0		    -1.644652

Mulliken charge is  0.318069

Radius for C,N,O is 1.50A and for H 1.45A (Breneman model as 
implemented in Gaussian98)

There is a large variability in the charges and I am wondering how to 
get a value which is acceptable. Further MD simulations will clearly 
depend on the charge values. I used UHF/LanL2DZ basis set on Fe and 
STO-3G for the atoms in the porphyrin ring.

I would really appreciate any suggestions on how to proceed in order to 
get acceptable charges for Fe.

Thank you,

Valentin Gogonea
Cleveland State University
Cleveland, Ohio, USA

More information about the gromacs.org_gmx-users mailing list