Polarizabilities and dispersion coefficients for alkali systems in second- and third-order perturbation

We have developed simple variational solutions for the first-order wavefunctions for alkali systems perturbed by a multipolar potential or an interatomic potential. These solutions are in conformity with the required asymptotic behaviour which is important in the analysis of the properties of atoms and ions at large separations. These wavefunctions are used to calculate polarizabilities, hyperpolarizabilities, and dispersion coefficients in second- and third-order perturbation. The second-order quantities are in agreement with established values. The third-order hyperpolarizabilities are in agreement with recent pseudopotential results. The third-order dispersion coefficients are expected to be considerably more accurate than earlier estimates.