Tests of approximate methods for the calculation of the static potential for electron scattering by CO

The interaction potential between an electron and an unperturbed CO molecule is calculated as a function of the electron's position r (measured with the origin at the center of mass of CO) by the INDO (intermediate-neglect-of- differential-overlap) molecular orbital theory and by an approximate application (following Itikawa and Takayanagi) of Massey's method. The results are compared quantitatively to the ab initia extended-basis-set molecular orbital calculation of Gianturco and Tait. The potential is expanded as F(r) = Σ_LV_L(r)P_L(r̂ · R̂), where R̂ is a unit vector along the internuclear axis. The INDO V _L(r) is fairly accurate for L =0,2, and 4 but not for L = 1. The approximate Massey's method calculation is fairly accurate only for r < 2.3 bohr for L = 0, 2, and 4.