Slater-type atomic orbital , definition

It is in the definition of the integrals or the lack of it, that most m.o. methods differ. The overlap integrals are easy to compute and were, indeed, tabulated for Slater-type atomic orbitals a long time ago (ref. 79). In some simple calculations, namely extended Huckel-type calculations a rough estimation of Hmn is as follows (see also page 79). 

By choosing the contracting scheme, it is possible to determine the contracted gaussian functions which best approximate Slater functions,88 Hartree-Fock atomic orbitals,89-90 etc. It should be noted that the size and balance (revealed, for example, by the optimum ratio of the number of s-type and p-type functions) of the basis are definite factors which control the quality of the final result (e.g., ref. 90). 

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