A uni®ed treatment of one-electron twocenter integrals over noninteger n Slater-type orbitals is described. Using an appropriate prolate spheroidal coordinate system with the two atomic centers as foci, all the molecular integrals are expressed by a single analytical formula which can be readily and compactly programmed. The analysis of the numerical performance of the computational algorithm is also presented.

A method for the calculation of one-electron two-center integrals is described. Using an ellipsoidal coordinate system, both the overlap, kinetic energy, and nuclear attraction integrals are expressed in terms of the so-called sigma function w introduced by Baba-Ahmed et al. A. Baba-Ahmed and J. Gayoso, Int. J. Quant. Chem. 23, Ž .Ž .x 71 1983 , Eq. 51 and which is easily programmed for a computer. The present investigation offers an advantage in that general formulas are derived which facilitate computation of the overlap and related two-center integrals over all Slater-type orbitals Ž . STOs with eventual nonintegral values of the principal quantum number. The proposed w algorithm permits to avoid the procedure of interpolation A. Baba-Ahmed and J.Ž .x Gayoso, Theor. Chim. Acta, 62, 507 1983 , Eqs. 11᎐14 used to overcome the difficulty introduced by the presence of nonintegral quantum numbers. Finally, numerical aspects of the proposed algorithm are analyzed and comparisons with other approaches are given.

The Huckel-London theory has been applied to the calculation of the "ring currents" octopole hypersusceptibilities of a series of conjugated compounds. Our calculations have been performed using fourth-order Rayleigh-Schrodinger perturbation technique. This is believed to be the first calculation of this kind. It is found that the values of "ring currents" hypersusceptibilities of fulvene and aiulene are larger, in absolute magnitude, than the values corresponding, respectively, to beniene and naphthalene. It is found that, in most cases, the "ring currents" hypersusceptibilities arc diamagnetic (negative values) for aromatic molecules and paramagnetic (positive values) for pseudoaromatic or antiaromatic compounds.