As expected by the El-Sayed's rule, the SOCs of GS/ 3 nπ * and 1 nπ * / 3 ππ * have sizable values of 98/13 and 113/14 cm -1 in the case of GMC-QDPT2 at PBE0 geometry, indicating that the SOC of S/T(M s = ±1) (the former value of /) are much bigger than that of S/T(M s = 0) (the latter value of /). This is because we chose a coordinate frame such that the ∆M S = ±1 SOC arises from the electron rotation of an in-plane orbital (e.g., the n orbital) to an out-of-plane orbital (e.g., the π and π * orbitals). As anticipated, the 1e contribution is much bigger than 2e.