Simulation of the influence of the core electrons by a pseudopotential. III. Calculation of the van der Waals forces

Two simple forms of pseudopotentials ( A and B) are compared as to their ability to reproduce Rydberg series and oscillator strengths for alkali atoms. Pseudopotential B turned out to be particularly satisfactory. A method for the calculation of intermolecular forces, based on the direct calculation of the asymptotic natural states of the interacting systems is introduced and applied in conjunction with the pseudopotential approach, to the long range interaction of alkali atoms. Extremely rapidly convergent expansions are obtained. The numerical results for the alkali pairs. based on pseudopotential B. agree surprisingly well with En values calculated semi- empirically by Dalgarno and Davison. E-8 and E-10 coefficients are also tabulated.