Relativistic effects in the electronic structure of the monoxides and monocarbonyls of Ni, Pd, and Pt: Local and gradient-corrected density functional calculations

Using a scalar relativistic version of the linear combination of Gaussian-type orbitals density functional method we have computed electronic and spectroscopic properties of the monoxides and monocarbonyls of Ni, Pd, and Pt. All-electron calculations with large basis sets were performed at both the local and the gradient-corrected density functional level. It is found that relativistic effects play a crucial role in Pt compounds, in particular as far as the metal-ligand distance is concerned. At the relativistic level the Pt-O and the Pt-CO distances are shorter than the corresponding Pd-O and Pd-CO bond lengths. Thus the trend in the metal-ligand distances is Ni<Pt<Pd. This is connected to a considerable relativistic strengthening of the Pt-O and Pt-CO bonds. Gradient corrections significantly reduce the computed binding energies, but are much less important for geometry and vibrational frequencies. They cause a more or less similar weakening and lengthening of the bonds which is quite independent of the metal considered.