Theoretical investigation of magnetically induced currents in closed-shell molecules

The work presented in this thesis is concerned with the theory and development of methods for ab initio calculation of magnetically induced current densities in closed-shell molecules. Two new methods are presented. The underlying theory of both methods is closely related to the theory of nuclear magnetic shielding (NMR) calculations. The Aromatic Ring-Current Shieldings (ARCS) method can be viewed as an experimental procedure in a theoretical framework. In the ARCS method, the strength of the magnetically induced ring current in aromatic molecules is extracted from the long-range part of the calculated NMR shielding function through a tting procedure. In the Gauge-Including Magnetically Induced Currents (GIMIC) method, the magnetically induced current density in molecules is calculated explicitly. In order to overcome problems with the dependence on the magnetic gauge origin, Gauge-Including Atomic Orbitals (GIAOs) are employed. The advantage of the GIMIC method is high accuracy, and the applicability to meaneld, density-functional and electron-correlated levels of theory. The GIMIC method is fast and can be applied to large closed-shell molecules of nano-technological importance. The method can also reveal the detailed structure of the current density in molecules. Using quadrature, the GIMIC method can be used to obtain the strength of induced currents in aromatic molecules. The ARCS and GIMIC methods have been applied to a variety of di erent molecular systems, both to test their applicability and accuracy, and in an attempt to understand and classify molecular aromaticity. List of publications List of publications included in the thesis I. J. Jusélius and D. Sundholm, Ab initio determination of the induced ring current in aromatic molecules, Phys. Chem. Chem. Phys., 1, 3429 (1999). II. J. Jusélius and D. Sundholm, The aromatic pathways of porphins, chlorins and bacteriochlorins, Phys. Chem. Chem. Phys., 2, 2145 (2000). III. J. Jusélius and D. Sundholm, The aromatic character of magnesium porphyrins, J. Org. Chem., 65, 5233 (2000). IV. J. Jusélius and D. Sundholm, The aromaticity and antiaromaticity of dehydroannulenes, Phys. Chem. Chem. Phys., 3, 2433 (2001). V. J. Jusélius, M. Straka, and D. Sundholm, Magnetic Shielding Calculations on Al2− 4 and Analogues, J. Phys. Chem. A, 105, 9939 (2001). VI. J. Jusélius, M. Patzschke, and D. Sundholm, Calculation of Ring-Current Susceptibilites for Potentially Homoaromatic Hydrocarbons, J. Mol. Struct. (Theochem), 633, 123 (2003). VII. J. Jusélius, D. Sundholm, and J. Gauss, Calculation of Current Densities using GaugeIncluding Atomic Orbitals, J. Chem. Phys., 121, 3952 (2004). List of other publications I. R. J. F. Berger, M. A. Schmidt, J. Jusélius, D. Sundholm, P. Sirsch, and H. Schmidbaur, Tetraberyllium-η4-oxo-hexa(arylcarboxylates), Z. Naturforsch. b, 56, 979 (2001). II. E. M. S. Maçôas, L. Khriachtchev, M. Petterson, J. Jusélius, R. Fausto, and M. Räsänen, Reactive vibrational excitation spectroscopy of formic acid in solid argon: Quantum yield for infrared induced trans→cis isomerization and solid state e ects on the vibrational spectrum, J. Chem. Phys., 119, 11765 (2004). III. M. Johansson and J. Jusélius, Arsole aromaticity revisited, Lett. Org. Chem. (2004), accepted. IV. L. Khriachtchev, J. Jusélius, A. Lignell, M. Räsänen, and E. Savchenko, Infrared absorption spectrum of matrix-isolated noble-gas hydride molecules: Fingerprints of speci c interactions and hindered rotation, J. Chem. Phys. (2004), accepted. V. D. Sundholm, M. Johansson, and J. Jusélius, Sphere currents of Buckminsterfullerene, Angew. Chem. Int. Ed. (2004), accepted. VI. Y. C. Lin, J. Jusélius, D. Sundholm, and J. Gauss, Calculation of Current Densities in Al2− 4 , Angew. Chem. Int. Ed. (2004), to be published.