Relativistic and Electron Correlation Effects as a Tool for Explaining Some Trends in Molecular Properties and Interactions

In this paper we discuss relatively routine Douglas–Kroll–Hess spin–free relativistic calculations as a tool for understanding some trends of molecular properties within the series of related molecules. Electron correlation effects are considered by the Coupled Cluster method with iterative treatment of the single and double excitation operators and perturbative treatment of triples, CCSD(T). For our analysis we use accumulated data on relativistic effects on ionization potentials, electron affinities and polarizabilities of the coinage elements, Cu, Ag, and Au and related series like Ia and IIa group elements. Next we analyze electric properties of diatomic molecules as CuF, AgF, and AuF, and compare electric properties and bonding energies of these molecules with intermetalics CuAl, AgAl, AuAl. Electric dipole moments and dipole polarizabilities of the series of oxides including a heavy atom, GeO, SnO, and PbO in their 1Σ ground states are also analyzed. Particular attention is paid to the dissociation energy of PbO and its electron affinity. The bonding character of the MeL series of complexes (Me=Cu, Ag, Au; L=H2O, NH3, and H2S) is explained by stressing the importance of the charge transfer from the lone pair of the ligand to the metal element. Relativistic effects which affect the Me electron affinity and polarizability facilitate understanding the trends of Me interactions with different ligands. We also mention using of the optimized virtual orbital space (OVOS) as an instrument which allows to circumvent problems with proper contraction needed for a specific approximate relativistic Hamiltonian. OVOS allows to reduce the computer time of correlated relativistic calculation by an order of magnitude.