Projection-operator calculations of the lowest e--He resonance

Computation of multicenter overlap integrals with Slater-type orbitals using psi(alpha)-ETOs

Multicenter overlap integrals appearing in the evaluation of multicenter-multielectron integrals of central and noncentral interaction potentials are calculated using complete orthonormal sets of psi(alpha)-ETOs (alpha=1, 0, -1, -2,...). The final results are expressed in terms of two-center overlap integrals between STOs. The convergence of the series is tested by calculating concrete cases for arbitrary quantum numbers, screening constants and location of STOs.

Improvements on the application of convergence accelerators for the evaluation of some three-electron atomic integrals

Convergence accelerator methods are employed to analyze some of the most difficult three-electron integrals that arise in atomic calculations. These integrals have an explicit dependence on the interelectronic coordinates, and take the form integral r(i)(1)r(j)(2)r(k)(3)r(l)(23)r(m)(31)r(n)(12) exp((-alpha(r1)-beta(r2)-gamma(r3))dr(1)dr(2)dr(3). The focus of the present investigation are the most difficult cases of the parameter set [i, j, k, l, m, n]. Several convergence accelerator techniques are studied, and a comparison presenting the relative effectiveness of each technique is reported. When the convergence accelerator approach is combined with specialized numerical quadrature methods, we find that the overall technique yields high-precision results and is fairly efficient in terms of computational resources. Difficulties associated with the standard numerical precision loss of convergence accelerator techniques are circumvented.