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Large Unit Cell (large + unit_cell)
Selected AbstractsSemiempirical LUC-INDO calculations on the effect of pressure on the electronic structure of diamondPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2007Ibtesam O. Radi Abstract A self-consistent LUC (large unit cell) formalism on the basis of semiempirical INDO (intermediate neglect of differential overlap) Hamiltonians has been used to study the electronic properties of diamond and to investigate the pressure dependence of these properties. The calculated properties are in good agreement with the experiments except the conduction-band width. The increase of pressure on diamond is predicted to cause the following effects; an increase of the valence and conduction-band widths with a decrease of the direct bandgap, an increase of the electronic occupation probability for the p-orbital with a decrease of this probability for the s-orbital, and a decrease of the X-ray scattering factor. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystallization and X-ray diffraction studies of inverting trehalose phosphorylase from Thermoanaerobacter sp.ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2010Annelies Van Hoorebeke Disaccharide phosphorylases are attractive enzymatic platforms for tailor-made sugar synthesis owing to their ability to catalyze both the synthesis and the breakdown of disaccharides. Trehalose phosphorylase from Thermoanaerobacter sp. (TP) is a glycoside hydrolase family 65 enzyme which catalyzes the reversible breakdown of trehalose [d -glucopyranosyl-,(1,1),- d -glucopyranose] to ,- d -glucose 1-phosphate and d -glucose. Recombinant purified protein was produced in Escherichia coli and crystallized in space group P212121. Crystals of recombinant TP were obtained in their native form and were soaked with glucose, with n -octyl-,- d -glucoside and with trehalose. The crystals presented a number of challenges including an unusually large unit cell, with a c axis measuring 420,Å, and variable diffraction quality. Crystal-dehydration protocols led to improvements in diffraction quality that were often dramatic, typically from 7,8 to 3,4,Å resolution. The structure of recombinant TP was determined by molecular replacement to 2.8,Å resolution, thus establishing a starting point for investigating the structural and mechanistic determinants of the disaccharide phosphorylase activity. To the best of our knowledge, this is the first crystal structure determination of an inverting trehalose phosphorylase. [source] Backscattering X-ray standing waves in the XUV regionJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2001T. M. Grehk It is demonstrated that Bragg reflection of XUV radiation can be used to study structural properties of crystalline materials with large unit cells. A standing-wave field is formed in a layered TiSe2 single crystal for a near-backscattering geometry (, = 88.5°). The partial electron yield is measured as a function of photon energy across the (001) Bragg reflection condition (h,, 1033,eV) and its characteristic modulation is compared with the results derived from dynamical diffraction theory in the two-wave approximation. The data reveal a large amount of disorder along the c -axis. [source] Surface and interface investigations using radioactive atomsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004K. Potzger Abstract The magnetic behavior of isolated nonmagnetic probe atoms (Cd) at ferromagnetic Ni surfaces and interfaces have been studied using perturbed angular correlation (PAC) spectroscopy. Atomic resolution is achieved making it possible to distinguish between probe atoms at various surface sites, i.e., in/at terraces, atomic steps, kinks. These different atomic surface sites have differing Ni coordination numbers, (i.e., the number of Ni nearest neighbours). With decreasing coordination number, a continuous nonlinear dependent correlation was found with increasing magnetic hyperfine fields (Bhf). Furthermore, experimental evidence is presented, that the induced s-moments on the Cd isolated impurity is independent of the details of the surface symmetry but essentially determined only by the coordination number. Finally, it has been observed that monolayers of Pd on Ni form large unit cells, which offer selected sites to the Cd impurity. We discuss this finding as basic research towards future applications with self-organizing patterned structures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||