Calculation of heats of formation for Zn complexes: Comparison of density functional theory, second order perturbation theory, coupled-cluster and complete active space methods

Heats of formation were predicted for nine ZnX complexes (X = Zn, H, O, F₂, S, Cl, Cl₂, CH₃, (CH₃) ₂) using 14 density functionals, MP2 calculations, and the CCSD and CCSD(T) coupled-cluster methods. Calculations utilized the correlation consistent cc-pVTZ and aug-cc-pVTZ basis sets. Heats of formation were most accurately predicted by the TPSSTPSS and TPSSKCIS density functionals, and the BLYP, B3LYP, MP2, CCSD, and CCSD(T) levels were among the poorest performing methods based on accuracy. A wide range of Zn₂ equilibrium bond distances were predicted, indicating that many of the studied levels of theory may be unable to adequately describe this transition metal dimer. To further benchmark the accuracy of the density functional methods, high-level CASSCF and CASPT2 calculations were performed to estimate bond dissociation energies, equilibrium bond lengths, and heats of formation for the diatomic Zn complexes, and the latter two quantities were compared with the results of DFT, MP2, and coupled-cluster calculations as well as experimental values.