Organodichalcogenide Structure and Stability: Hierarchical Ab Initio Benchmark and DFT Performance Study

We conducted a double-hierarchical ab initio benchmark and DFT performance study of the organodichalcogenide bonding motif CH₃Ch¹-Ch²(O)_nCH₃ with Ch¹, Ch² = S, Se and n = 0, 1, 2. The organodichalcogenide model systems were optimized at ZORA-CCSD(T)/ma-ZORA-def2-TZVPP. Our ab initio benchmark involved a hierarchical series of all-electron relativistically contracted variants of the Karlsruhe basis sets (ZORA-def2-SVP, ZORA-def2-TZVPP, ZORA-def2-QZVPP), both with and without diffuse functions (ma-basis set), in conjunction with a hierarchical series of ZORA-relativistic quantum chemical methods [HF, MP2, CCSD, and CCSD(T)]. Counterpoise correction was applied to account for the basis set superposition error (BSSE). We assessed the performance of 33 ZORA-relativistic DFT functionals (ZORA-[XC functional]/TZ2P//ZORA-[XC functional]/TZ2P) against our benchmark energies and found that M06 and MN15 furnish accurate geometries and bond energies within a mean absolute error of 1.2 kcal mol⁻¹ relative to our best ab initio reference data.