Universal basis sets of elliptical functions. Applications to simple diatomic molecules

The use of universal basis sets of elliptical functions in molecular electronic structure calculations for diatomic systems is investigated. It is demonstrated that the same integrals over elliptical basis functions can be employed in calculations at a range of internuclear separations, for low-lying excited states and for a range of nuclear charges. Universal basis sets of elliptical functions are shown to lead to accurate energy gradients. Applications to one- and two-electron systems are reported together with a calculation on the helium dimer.