The resulting matrix series are convergent, as the overlap integrals satisfy |S a b | = |S b a | < 1, and their numerical values can be calculated iteratively to any given accuracy, (provided that the accuracy of the pre-computed overlap integrals S is sufficient). However, it is also possible to calculate their values analytically. To this end, it is conve-nient to introduce new matrices Γ and Λ with elements