The effect of different scalar relativistic schemes on the SOC-MRSF results was investigated on the fifth-row element Sn and the results are presented in Table . Since the scalar relativistic effects are included during the orbital optimization process, in principle it can have a profound effect on the final relativistic energies. Although it is mostly due to error cancellations, the prediction by M06-2X functional in combination with the x2c-TZVPall basis set is quite accurate for Sn in Fig. ). Therefore, SOC-MRSF calculations were performed with M06-2X/x2c-TZVPall for the investigations. Although the higher order Douglas-Kroll (DK) transformation generally improves the accuracy, the order has little effect on the Sn 3 P 0 -3 P 1 gap. While the IOTC (infinite-order two-component method) shows a similar small 3% error, the RESC (relativistic elimination of small component) transformation somewhat deteriorates the agreement. Since the aforementioned error cancellation is still valid, it would be a good practice to check the particular combination of functional, basis sets, and scalar relativistic transformation against available experimental atomic spectra, especially for the heavy atoms, before applying SOC-MRSF. Ovrall, the SOC-MRSF with BH&HLYP/cc-pVTZ appears to be a magic choice upto fourth-row elements, while M06-2X/x2c-TZVPall can produce good results for fifth-row ones.