ALTERNATIVE BASIS FUNCTIONS FOR L2 CALCULATIONS ON THE MOLECULAR CONTINUUM .1. THE BASIC PROTOTYPE INTEGRALS

Alternative square-integrable (L2) basis functions, the oscillating Hermite Gaussian functions (OHGF's), are proposed for describing the continuum orbitals in L2 calculations on molecules. Each function is the product of a Hermite Gaussian function (HGF), which gives the proper dumping and angular factor, and a radial trigonometric function, cos(kr), which describes the oscillating asymptotic behavior of a continuum orbital. Analytic expressions for the one- and two-electron integrals involving s-type OHGF's and many-center s-type HGF's are derived and their numerical implementation is discussed in detail. The present proposal of adopting a mixed basis set of OHGF's and many-center HGF's for the L2 description of bound and continuum molecular states is compared with the other types of basis functions currently employed. With respect to these, it requires a greater computational effort in the integral evaluation, but it also allows an accurate description of the electronic continuum in general polyatomic systems.