Ab initio calculations of the structures and vibrational spectra of ethene complexes

To facilitate an objective comparison of the efficacy of the simulation of structural parameters and vibrational spectra of transition-metal complexes of commonly used ab initio methods, the geometries of the ethene complexes of Ni(0) and Ni(H) have been optimized using both ab initio and density functional theory (DFT) calculations and a wide variety of basis sets. The harmonic vibrational spectra of [Ni(C2H4)] and [Ni(C2H4)](2+) have been evaluated from the optimized geometries at Hartree-Fock, post-Hartree-Fock Moller-Plesset perturbation theory, MP2, and a range of DFT functionals. Upon comparison with experimental data, it has been found that hybrid DFT functionals, specifically B3-LYP, afford the most accurate fit to the experimental data. This is especially the case when using the all-electron DZVP basis set, which provides highly accurate results. The use of the effective core potential LanL2DZ basis set has been found to achieve a comparable level of accuracy to the DZVP basis set, at a fraction of the computational efficiency. Extension of these calculations to ethene complexes of other transition metals has revealed trends in their structures and vibrational spectra.