Calculation of the energy levels of barium using B splines and a combined configuration-interaction and many-body-perturbation-theory method

A recently developed method of precise atomic calculations [Phys. Rev. A 54, 3948 (1996)] which combines many-body perturbation theory with the configuration-interaction method is used to calculate the 24 lowest energy levels of Ba. B-spline functions in a cavity of a finite radius are used as a unified many-purpose basis set. The calculation reproduces the experimental removal energies for Ba within a fraction of a per cent. Advantages of the new method and B splines are discussed.