Structure and Excitation Spectra of Third-Row Transition Metal Hexafluorides Based on Multi-Reference Exact Two-Component Theory

The structures and some vertical excitation energies of third-row transition metal hexafluorides (MF6, M = Re, Os, Ir, Pt, Au, Hg) were calculated using the multi-reference configuration interaction (MRCI) theory based on exact two-component (X2C) Hamiltonian. The spin-orbit coupling (SOC) was variationally included at the Hartree-Fock level, enabling us to analyze the SOC at the orbital level. The excitation spectra were assigned based on the double group, a relativistic group theory applicable to states with the SOC. This study provides a fundamental understanding of the ligand field splitting, including the SOC, that is useful for the photochemistry and spin chemistry involving heavy elements.