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Browsing Department of Chemistry and Biochemistry by Author "Alkan, Fahri"
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Item Calculation of chemical-shift tensors of heavy nuclei: a DFT/ZORA investigation of 199Hg chemical-shift tensors in solids, and the effects of cluster size and electronic-state approximations(Royal Society of Chemistry, 2014-06-02) Alkan, Fahri; Dybowski, Cecil; Fahri Alkan and C. Dybowski; Alkan, Fahri; Dybowski, C.Calculations of the nuclear magnetic resonance chemical-shielding tensors of a suite of mercury-containing materials using various cluster models for the structures provide a stringent test of the procedures for forming models and for calculation with various methods. The inclusion of higher co-ordination shells in the molecular clusters permits quantum chemical calculations of 199Hg chemical-shielding tensor elements within 3% of the experimental values. We show that it is possible to reduce the size of computationally expensive molecular-cluster calculations with limited effect on calculated NMR parameters by carefully introducing the frozen core approximation. The importance of the relativistic Hamiltonian for accurate predictions of chemical-shielding values is demonstrated within the molecular cluster approach. The results demonstrate that careful design of a cluster to represent the solid-state structure, inclusion of relativistic components in the Hamiltonian at least at the spin–orbit level, and judicious use of approximations are essential to obtain good agreement with experimental results.Item Chemical-shift tensors of heavy nuclei in network solids: a DFT/ZORA investigation of 207Pb chemical-shift tensors using the bond-valence method(Royal Society of Chemistry, 2015-09-02) Alkan, Fahri; Dybowski, Cecil; Fahri Alkan and C. Dybowski; Alkan, Fahri; Dybowski, CecilCluster models are used in calculation of 207Pb NMR magnetic-shielding parameters of α-PbO, β-PbO, Pb3O4, Pb2SnO4, PbF2, PbCl2, PbBr2, PbClOH, PbBrOH, PbIOH, PbSiO3, and Pb3(PO4)2. We examine the effects of cluster size, method of termination of the cluster, charge on the cluster, introduction of exact exchange, and relativistic effects on calculation of magnetic-shielding tensors with density functional theory. Proper termination of the cluster for a network solid, including approximations such as compensation of charge by the bond-valence (BV) method, is essential to provide results that agree with experiment. The inclusion of relativistic effects at the spin–orbit level for such heavy nuclei is an essential factor in achieving agreement with experiment.