SiO bonded interactions in coesite: a comparison of crystalline, molecular and experimental electron density distributions |
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Authors: | K M Rosso G V Gibbs M B Boisen |
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Institution: | (1) Departments of Geological Sciences, Materials Science and Engineering and Mathematics Virginia Tech, Blacksburg, VA 24061, |
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Abstract: | Bond critical point properties of electron density distributions calculated for representative Si5O16 moieties of the structure of coesite are compared with those observed and calculated for the bulk crystal. The values calculated
for the moieties agree with those observed to within ∼5%, on average, whereas those calculated for the crystal agree to within
∼10%. As the SiOSi angles increase and the SiO bonds shorten, there is a progressive build-up in the calculated electron density
along the bonds. This is accompanied by an increase in both the curvatures of the electron density, both perpendicular and
parallel to each bond, and the Laplacian of the electron density distribution at the bond critical points. The cross sections
of the bonds at the critical points become more circular as the angle approaches 180o. Also, the bonded radius of the oxide
anion decreases about twice as much as that of the Si cation as the SiO bond length decreases and the fraction of s-character of the bond is indicated to increase. A knowledge of electron density distributions is central to our understanding
of the forces that govern the structure, properties, solid state reactions, surface reactions and phase transformations of
minerals. The software (CRYSTAL95 and TOPOND) used in this study to calculate the bond critical properties of the electron
density and Laplacian distributions is bound to promote a deeper understanding of crystal chemistry and properties.
Received: 23 February 1998 / Revised, accepted: 16 July 1998 |
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Keywords: | Coesite Electron density Critical point properties Laplacian SiO bond |
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