<p>First-principle-based quantum chemical methods are employed to characterise the transition metals chalcogen–chalcogen bonds of the types M(HCh)₂²⁺ and M(ChCH₃)₂²⁺ (Ch = S, Se) in the gas phase. Use of such model systems allow us to calculate the binding energy values considering a very large basis set along with density functional theory (DFT) based methods and compare these values with corresponding values at MP2, CCSD, and CCSD(T) methods. In this work, DFT and post-Hartree–Fock wave function methods including MP2, CCSD, and CCSD(T) are used to calculate the binding energy using the 6-311++G(2d,2p) basis set. Error analysis performed for BLYP, SVWN, TPSS, M05, MPW1PW91, B3LYP, B3LYP-D, B3LYP-D3, M06-HF, MO8-HX, MN-15, LC-ωHPBE, ωB97XD, MP2, and CCSD methods using the CCSD(T) results as the reference. M06-HF, MN-15, LC-ωHPBE, MO8-HX, MN-15, and MPW1PW91 outperformed other DFT functionals. MP2, in case of small molecules like M(HCh)₂²⁺ and M(ChCH₃)₂², reflects poor performance because of its inability to capture significant electron correlation effects inherent to transition–metal complexes compared to CCSD and CCSD(T) methods. The results offer valuable insights into metal–ligand interactions, guiding future studies in catalyst optimization and electronic structure modelling.</p> Graphical abstract <p>This study employs DFT and post-Hartree–Fock wave functional methods (MP2, CCSD, CCSD(T)) to characterize M(HCh)₂²⁺ and M(ChCH₃)₂²⁺ (M = Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺; Ch = S, &amp; Se) complexes in the gas phase. Error analysis identifies M06-HF, MN-15, LC-ωHPBE, and MO8-HX as the best-performing functionals. The findings provide valuable insights into metal-ligand interactions that may help in catalyst design and electronic structure modelling for transition-metal systems.</p>