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

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Abstract
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.