SO approximation underestimate/overestimate the energy gaps within the ground/firstexcited multiplets of about -5%/+100% with respect to H BP SO , while the SOC mean field approximation well reproduces the results for the ground 6 H 15/2 level, and slightly underestimates (µ ≈ -3) the gaps within the excited 6 H 13/2 level, for both the multi-center and one-center 2e-SOC integrals evaluations. H ABP SO leads to almost negligible errors in all cases.