Multipole Analysis of the Electron Density in Topaz Using X-ray Diffraction Data

The static deformation electron density, Laplacian of the electron density and critical points in the electron density were analyzed in topaz Al₂[SiO₄]F₂, using high-precision X-ray diffraction data. The electron deformation density, positive values of the Laplacian at (3,-1) bond critical points and the net atomic charges indicate a closed-shell-type interaction in the polyhedra. Anion valence-shell charge depletions are revealed. Maxima in the Laplacian of the electron density are displaced towards the close-packed plane owing to the mutual repulsion of the anion valence shells. The relationship between the topological features of the electron density and the close-packing concept is discussed. Shifts of the critical points from the internuclear vectors reflect the strain in the structure.

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