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.

• Received 17 October 1997

DOI:https://doi.org/10.1103/PhysRevA.57.2459