(1) SO versus ∆E = 38742, 38779, 38807, 38849 cm -1 by H BP SO , with µ ≈ -9% and σ ≈ 0.1%). On the other hand, H MF SO approximation leads to errors within the acceptable range ±4%, with generally small standard deviations (σ < 1%). As for the ground multiplets, H MF SO and H AMF SO approximations lead to very comparable results, and H ABP SO shows almost zero errors.