Biomedical subjects

Vladimir Tsirelson

Publications and source records attributed to Vladimir Tsirelson.

3 recordsLinked to original sources

PubMed2005

X-ray diffraction by a crystal in a permanent external electric field: electric-field-induced structural response in alpha-GaPO4.

For the first time, site-selective distortion has been investigated for two different structural units in the ternary compound alpha-GaPO(4) under the influence of a permanent external electric field. Based on 54 measured reflection intensities, the electric-field-induced distortion of PO(4) and GaO(4) tetrahedra in alpha-GaPO(4) crystals is evaluated using a model of pseudoatomic displacements introduced recently [Gorfman, Tsirelson & Pietsch (2005). Acta Cryst. A61, 387-396]. A stronger variation of the P-O bond lengths in the PO(4) tetrahedron was found compared to the bonds in the GaO(4) tetrahedron. The different distortions of the tetrahedra owing to the electric field were analysed in terms of the valence charge density of alpha-GaPO(4) and its topological characteristics. The larger charge of the P pseudoatom compared to the Ga atom was recognized as the main reason for the higher sensitivity of the PO(4) tetrahedron to a permanent external electric field.

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PubMed2004

On functions and quantities derived from the experimental electron density.

Calculation of properties of molecules and crystals as obtained from a multipole electron-density model restored from the accurate X-ray diffraction data is considered. Electronic and exchange energy-density distributions are presented along with those of local temperature and local entropy. Integration of the local functions over atomic basins defined by the zero-flux condition allows properties of molecules and crystals to be expressed in terms of atomic contributions derived directly from X-ray diffraction experiments. Distributions of local Fermi momentum and one-electron potential are considered as well. The approach has been applied to diamond, sodium fluoride, sodium chloride, solid chlorine, alpha-oxalic acid dihydrate and YBa(2)Cu(3)O(6.98).

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PubMed2002

Analyzing experimental electron density with the localized-orbital locator.

The localized-orbital locator, which describes the features of bonding in terms of the local kinetic energy, is approximately expressed as a function of electron density and its first and second derivatives. Calculations based on accurate electron densities derived from X-ray diffraction data are carried out for crystals with different types of chemical bonds. It is demonstrated that the localized-orbital locator reveals the features of atomic interactions in a solid state and allows the covalent, ionic and van der Waals bonds to be distinguished.

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