Unless otherwise explicitly mentioned, we optimized the two axial and four equatorial M-F bonds of MF 6 molecules, assuming they belong to the O h or D 4h symmetry group. The SURFIT program was used to obtain the equilibrium structure in a two-dimensional potential energy surface for several molecules. Numerous one-point calculations were performed for the other molecules by changing the bond length by a step size of 0.001 Å. The details are explained in the Supporting Information. The O h structure was obtained using the twofit program, which is a utility of the DIRAC code. The projection analysis using the intrinsic atomic orbital was carried out for the PtF 6 molecule. At the SF level, two electrons are distributed in four orbitals, and 130 electrons occupy the closed shell in the AOC-HF calculation. In the projection analysis step, 0.01 and 1.99 electrons are distributed in the virtual e ′ g and e g orbitals and the occupied b 2g orbitals to obtain the gross population of the virtual e ′ g orbitals. At the SO level, 132 electrons occupy the closed shell in the HF calculation. In the projection analysis step, 0.01 (3.99) electrons are distributed in the virtual u ′ 3/2,g and e 5/2,g orbitals (the occupied u 3/2,g orbitals) (cf., Figure ). In the atomic and molecular calculations, an option of the DIRAC code, .OPENFAC=1.0, was employed.