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Small Gaussian expansions of Slater-type orbitals by the method of least squares are presented. Expansion lengths are from one to six. Slater-type orbitals 1s through 5g are included. The least-squares equations were solved by a full-matrix method. Expectation values, r−2, r−1, r, and r2 for the several expansions are tabulated. Orbital products of the small Gaussian expansions have been Fourier analyzed and are satisfactory for x-ray scattering analysis of x-ray diffraction data or of molecular wavefunctions comprised of extended STO basis sets.
Robert F. Stewart (1970) studied this question.