The electronic properties of [Fe(SCH3)(4)](-2-), a model for the iron-sulfur site in rubredoxin, and the conformational dependence of these properties were investigated with ab initio calculations. The calculations were done at the unrestricted Hartree-Fock level with various basis sets, and the effects of electron correlation were tested in some calculations using second-order perturbation theory. The conformational dependence was studied using five conformations of the model complex that differed by rotations about the Fe-S and C-S bonds. Geometry optimizations showed that these bond lengths changed little among the conformations examined, except where steric crowding existed. The atomic spin populations and spin contamination values (S-2) were also homogeneous among the conformations. The relative energies of all but one of the conformations were very small in both the oxidized and reduced states; thus, the total energy changes upon reduction, Delta E-redox, of all but one of the conformations were within 30 mV of each other. The exception was about 100 mV less negative than the other four structures and represents a less likely dihedral rotation transition state. More important, the difference of only 30 mV between conformations similar to that of the iron-sulfur site in rubredoxin and in the Holm-Ibers analogue indicates that very little of the 800 mV difference in redox potential between rubredoxin and in the Holm-Ibers analogue can be attributed strictly to conformationally dependent differences in electronic structure. In addition, atom-centered partial charges were determined by Mulliken’s method and two different electrostatic potential (ESP) fitting methods : the surface-based geodesic tessellation method and the grid-based CHELPG method. For all three methods, the partial charge distributions showed little conformational dependence. Moreover, the Mulliken charges, which are not subject to the problems of buried atoms associated with ESP methods, indicate very little conformational dependence. The CHELPG partial charges were selected as being the most reasonable for ESP calculations; thus, a geometry independent set of CHELPG partial charges is proposed.