Relativistic quantum chemistry calculations for heavy element compounds often employ effective core potentials (ECP). Without the core electrons and orbitals, the core-valence two-electron SOC screening can be described using effective nuclear charges (ENC). The SBKJC ECP and its associated ENCs were used with SOC-MRSF to calculate the 3 P 1 -3 P 0 gaps of the Group 14 elements from C to Sn, and the results are listed in Table , along with the ENC values. The PBE0 functional was utilized in the calculations. Only one-electron contribution is included in the SOC calculations and Pauli-Breit 1st order relativistic corrections were applied to it. This is because the ENCs were devised based on this combination. Using the ENC developed by Koseki et al. , excellent agreements with experiments are seen from the results of C, Si and Ge atoms (less than 5% errors).