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Multipole-refined charge density study of diopside (Abstract/Poster in atti di convegno)

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Multipole-refined charge density study of diopside (Abstract/Poster in atti di convegno) (literal)

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Bianchi, R.; Forni, A.; Oberti, R. (2005)
Multipole-refined charge density study of diopside
in XX Congress of the International Union of Crystallography, Firenze
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he electron density distribution of diopside at ambient conditions has been determined by X-ray diffraction and refined through the multipole model of electron density, following the formalism of Stewart [1]. The final multipole refinement includes two extinction parameters, according to the Sabine model, and two kappa expansion/contraction parameters (one for O and the other for Si, Ca and Mg valence monopoles). The expansions over the spherical harmonics were truncated at the octopole level. Topological analysis of the electron density and its Laplacian distributions [2] reveals that the four SiO bonds are intermediate between ionic and covalent bonds, clearly different from the MgO and CaO bonds. Determination of the atomic basins results in charges of +3.2(2)e on Si and 1.6(1)e, on average, on the oxygen atoms. The charges of cations are very close to the corresponding formal ones. The results are compared with those previously obtained on spherically averaged or maximum entropy method charge densities of diopside. The program VALTOPO [3] was used for refinements and topological analysis of the experimental density. [1] Stewart R. F., Acta Crystallogr. Sect. A, 1976, 32, 565. [2] Bader, R. F. W., Atoms in Molecules - A Quantum Theory, Oxford University Press: Oxford, 1994. [3] Bianchi, R., Forni, A. J. Appl. Crystallogr., 2005, 38, 232. (literal)

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