Efficient $6j$ symbol evaluations for atomic calculations

Abstract

We have developed an efficient tabulation scheme to evaluate $6j$ symbol for atomic calculations. The scheme is appropriate for coupled-cluster based calculations. In particular, for perturbed coupled-clusters calculations, which has another perturbation in addition to the residual Coulomb interaction. The scheme relies on the symmetry of the $6j$ symbol and the triangular conditions.

5 pages and 6 figures