Browsing by Author "Kiwi, M."

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    Is NMR the tool to characterize the structure of C20 isomers?
    (2002) Romero, A.H.; Sebastiani, D.; Ramírez, R.; Kiwi, M.
    We investigate the feasibility of using nuclear magnetic resonance (NMR) chemical shift calculations as a tool to provide structural information for C-20 fullerene type molecules. NMR chemical shifts are extremely sensitive to the local chemical environment of an atom, reflecting unambiguously its bond lengths and angles as well as its hybridization. Thus, they can distinguish between the different isomers that are candidates for the ground state of this molecule. We calculate the NMR shifts for several C-20 isomers and show that NMR constitutes a potential tool to discriminate and identify experimentally a particular C-20 molecular conformation, and also the level of theory which best describes the experimental structure. (C) 2002 Elsevier Science B.V. All rights reserved.
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    Surface states of FeF2 (110) and its uncompensated magnetization
    (2015) Munoz, F.; Romero, A. H.; Mejia-Lopez, J.; Roshchin, Igor V.; Gonzalez, R. I.; Kiwi, M.
    The (110) surface of iron fluoride (FeF2) is especially relevant to the understanding of the exchange bias phenomenon, which has important applications in the sensor industry, and has been extensively explored, both theoretically and experimentally. Here we investigate this FeF2 surface by means of oh mine techniques. We compute the (110) surface reconstruction, energetics, magnetic moments, band structure, charge density and electron localization function, for the two possible terminations (Fe and F). The surface reconstruction modifies the atomic and electronic structure of the free surface, yielding magnetism of a magnitude of 0.1 mu(B) per surface unit cell. Moreover, the charge density also changes, which alters the bonding in the vicinity of the surface. All these changes are expected to be relevant for exchange bias, that is once a ferromagnetic layer is deposited on the FeF2 surface. (C) 2015 Elsevier B.V. All rights reserved.