Browsing by Author "Schreckenbach, Hans Georg"
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- ItemOpen AccessRelativity and magnetic properties: a density functional study(1996) Schreckenbach, Hans Georg; Ziegler, TomThis thesis has two major, related subjects, relativity and magnetic properties. All the investigations are based on density functional theory (DFf). An algorithm has been developed and implemented that allows the determination of relativistic energy gradients. This implementation enables automated geometry optimization at the relativistic level. The scheme has been applied to the calculation of M-CO bond lengths and first bond dissociation energies in binary transition metal carbonyls. A unique program system has been developed that allows the calculation of NMR shieldings and EPR g-tensors. The program is based on the use of "gauge including atomic orbitals" (GIAO). Expressions have been derived for the extension of the program to include the frozen core approximation, a scheme in which only the valence electrons are treated explicitly, and scalar relativistic effects. These expressions have been implemented into the DFf-GIAO program. The program has been applied to the chemical shift in systems ranging from small first row compounds to the metal chemical shift in transition metal carbonyls M(CO)6. This represents the first calculation of heavy element shifts that is based on a relativistic first principle quantum mechanical method. The calculated metal shifts of M( CO)6, taken relative to [MO4] 2-, are -1,846, -1804, and -3615 ppm for M = Cr, Mo, W, respectively. The corresponding experimental values are -1,795, -1,857, and -3,505 ppm. The inclusion of relativity is crucial for a proper description of ligand and metal shifts in 5 d complexes. Various aspects of NMR shielding calculations are discussed in this thesis. They comprise basis set requirements, exchange-correlation functionals, the importance of core orbitals, relativistic effects, the relation of the GIAO method to the common-gauge scheme, among others. Certain limitations of the method and possible future directions have been considered as well. The DFf-GIAO NMR program has been extended to include the calculation of the EPR g-tensor. This extension is the first GIAO and the only first principle DFT program for the g-tensor. The program is validated by calculations of g-tensors for a comprehensive set of small radicals.