Perturbation calculations of nonexpanded interactions in small atomic and molecular systems

Abstract

The N-term representation of the H atom static propagator in terms of a finite discrete set of linear excited pseudostates involving positive powers of the radial variable is used to calculate multipole components of nonexpanded induction and dispersion interactions at the bond length for H⁺ ₂ and H₂, nonexpanded dispersion coefficients for H₂, and hydrogenic second-order energy for the He sequence. Even if convergence is sensibly slower than that observed for expanded perturbations, the N = 20 approximation is found to give results at worst within 1% of the accurate reference values from the literature.