[gmx-users] CHelpG charge for Fe

Marc Baaden baaden at smplinux.de
Wed Nov 13 10:00:30 CET 2002

Hi Valentin,

I did gaussian 98 calculations on Fe(III). Here are my notes
concerning the radii that I used. Hope it helps,


For iron there are several ionic radii. Let's use radii from

o    Fe(III) 6-coordinate, octahedral 69 pm

o    Fe(III) 6-coordinate, octahedral, high spin 78.5 pm

Note: The "efective ionic radii" quoted here assume that the ionic
radius of F- is 133 pm and that of O2- is 140 pm. The values for iron
thus correspond quite well to che tabulated Gaussian Merz-Kollman
radii, and will be scaled for Francl and Breneman, with a mean factor
for F- and O2-. Values depend upon the coordination number and for
d-block metals on the fact whether or not the metal is in a high or
low spin state.

Atomnb        AtTyp         Merz-Kollman  Francl        Breneman
                                          (CHELP)       (CHELPG)
............. ............. ............. ............. .............
26            Fe            0.69          0.75          0.85
26            Fe            0.785         0.85          0.97
              high spin

>>> Valentin Gogonea said:
 >> Hi GMX users,
 >> Does anybody has a suggestion about what radius to use for Fe(2+) and 
 >> Fe(3+) when doing ab initio CHelpG calculations. This radii are not 
 >> available in G98.
 >> Thank you.
 >> Valentin
 >> CSU
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Marc Baaden

 Dr. Marc Baaden - Laboratory of Molecular Biophysics, Oxford University
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