In the case of the heaviest fifth-row element Sn, the accuracy of the M06-2X functional appears to be much better than BH&HLYP. Due to its strong SOC, the adoption of x2x-TZVPall basis sets has a high impact, yielding an excellent accuracy with ∼ 3% error. However, the good agreement of Sn can be due to an error cancellation. A source of error in our SOC-MRSF scheme comes from the perturbative SOC treatment, which is limited to the L-S coupling for all these atoms. While such a coupling scheme works well for light-weighted elements, it fails to describe heavy elements with much stronger SOC. The alternative j-j coupling is more appropriate in those cases. For such a situation, SOC needs to be included in the orbital optimization step, generating spinors that mix α and β spin functions. This non-perturbative SOC scheme requires two-component atomic orbitals as basis sets and is beyond our current SOC-MRSF scheme. Nonetheless, it is quite remarkable that the overall accuracy with less than 10% error is achieved by our SOC-MRSF-TDDFT up to the fifth row in the periodic table. And the SOC-MRSF splittings compare favorably with the 4c-CASSCF and 4c-CASPT2 results.