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

We have developed simple variational solutions for the first-order wavefunc tions for alkali systems perturbed by a multipolar potential or an interato mic potential. These solutions are in conformity with the required asymptot ic behaviour which is important in the analysis of the properties of atoms and ions at large separations. These wavefunctions are used to calculate po larizabilities, hyperpolarizabilities, and dispersion coefficients in secon d- and third-order perturbation. The second-order quantities are in agreeme nt with established values. The third-order hyperpolarizabilities are in ag reement with recent pseudopotential results. The third-order dispersion coe fficients are expected to be considerably more accurate than earlier estima tes. (C) 1999 Elsevier Science B.V. All rights reserved.