The single charging integral method, recently employed to calculate residual chemical potential differences between water and methanol due to size, energy, and partial charge parameters, is extended to include the contributions due to the differences in molecular model geometry. The calculated infinite dilution activity coefficients for the binary are compared to their experimental values at 298 K. With the SPC water model and the methanol model of Van Leeuwen [Van Leeuwen and Smit, J. Phys. Chem. 99 (1995) 831], the total calculated residual chemical potential difference between water and methanol agrees to within 2% of the experimental value. The residual chemical potential differences in the infinite dilution systems, however, disagree with experiment by 20 to 100%. The effect of deviations from the Lorentz-Berthelot combining rules for unlike site-site interactions is addressed. The delicate balance between electrostatic attraction and overlap repulsion is implicated in the disagreement between the calculated and experimental chemical potential differences.