Configurational inversion of the tetrahedral molecules CH₄, SiH₄, and GeH₄

We discuss from computed density functional theory energies as well as Hartree-Fock, Kohn-Sham, and their hybrid combinations how the configurational inversion of the tetrahedral AH₄ molecules CH₄, SiH₄, and GeH₄ takes place. In contrast to methane, the configurational inversion of which can occur via a C_s transition state, both silane and germane can undergo configurational inversion via a square-planar D_4h transition state. The activation energy for the inversion is 109.4, 88.6, and 93.7 kcal/mol in methane, silane, and germane, respectively, at the B3LYP/6-311G** level of theory. Walsh diagrams are analyzed to increase our knowledge with respect to the configurational inversion of these tetrahedral molecules in terms of one-electron orbitals. The way of configurational inversion is strictly determined by which of the "nonbonding" a_2u and b_1g orbitals in the D_4h structures is occupied by a pair of electrons.