Gaussian expansions of orbital products for the evaluation of two-electron integrals

A method is described for evaluating multicenter integrals over contracted gaussian-type orbitals by the use of gaussian expansion of orbital products. The expansions are determined by the method of non-linear least squares with constraints. There is no restriction upon the symmetry of the orbital product and the method is applicable to all products arising from s, p and d-type orbitals. Results are given to indicate the accuracy of the method.