The 𝑘 4$$5 <=>%$ and 𝜙 7 are the force constant and the equilibrium angle of the harmonic potential, and the 𝑘 4$$5 <=>%$ value was set to 1.79 × 10 4 kcal/ (mol Å 2 ) (8.0 au). By carefully tuning 𝑟 7 and 𝜙 7 in a VL, both the LTEP and the pyramidalization parameter of real phosphorus(III) ligands can be reproduced (see Figure for detail). It should be noted that, although the 𝑟 7 and 𝜙 7 values to reproduce electronic effects of a given ligand slightly changes depends on the choices of the force constants (𝑘 4$$5 and 𝑘 4$$5 <=>%$ ), this would not affect the accuracy of the approximation as long as the LTEP and the pyramidalization parameter are reproduced.