Acta Crystallographica Section A
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Acta Crystallographica Section A: Foundations and Advances covers theoretical and fundamental aspects of the structure of matter. The journal is the prime forum for research in diffraction physics and the theory of crystallographic structure determination by diffraction methods using X-rays, neutrons and electrons. The structures include periodic and aperiodic crystals, and non-periodic disordered materials, and the corresponding Bragg, satellite and diffuse scattering, thermal motion and symmetry aspects. Spatial resolutions range from the subatomic domain in charge-density studies to nanodimensional imperfections such as dislocations and twin walls. The chemistry encompasses metals, alloys, and inorganic, organic and biological materials. Structure prediction and properties such as the theory of phase transformations are also covered.enCopyright (c) 2017 International Union of Crystallography2017-09-13International Union of CrystallographyInternational Union of Crystallographyhttp://journals.iucr.orgurn:issn:2053-2733Acta Crystallographica Section A: Foundations and Advances covers theoretical and fundamental aspects of the structure of matter. The journal is the prime forum for research in diffraction physics and the theory of crystallographic structure determination by diffraction methods using X-rays, neutrons and electrons. The structures include periodic and aperiodic crystals, and non-periodic disordered materials, and the corresponding Bragg, satellite and diffuse scattering, thermal motion and symmetry aspects. Spatial resolutions range from the subatomic domain in charge-density studies to nanodimensional imperfections such as dislocations and twin walls. The chemistry encompasses metals, alloys, and inorganic, organic and biological materials. Structure prediction and properties such as the theory of phase transformations are also covered.text/htmlActa Crystallographica Section A: Foundations and Advances, Volume 73, Part 6, 2017textweekly62002-01-01T00:00+00:006732017-09-13Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section A: Foundations and Advances427urn:issn:2053-2733med@iucr.orgSeptember 20172017-09-13Acta Crystallographica Section Ahttp://journals.iucr.org/logos/rss10a.gif
http://journals.iucr.org/a/issues/2017/06/00/isscontsbdy.html
Still imageAbout difference electron densities and their properties
http://scripts.iucr.org/cgi-bin/paper?sc5109
Difference electron densities do not play a central role in modern phase refinement approaches, essentially because of the explosive success of the EDM (electron-density modification) techniques, mainly based on observed electron-density syntheses. Difference densities however have been recently rediscovered in connection with the VLD (Vive la Difference) approach, because they are a strong support for strengthening EDM approaches and for ab initio crystal structure solution. In this paper the properties of the most documented difference electron densities, here denoted as F − Fp, mF − Fp and mF − DFp syntheses, are studied. In addition, a fourth new difference synthesis, here denoted as {\overline F_q} synthesis, is proposed. It comes from the study of the same joint probability distribution function from which the VLD approach arose. The properties of the {\overline F_q} syntheses are studied and compared with those of the other three syntheses. The results suggest that the {\overline F_q} difference may be a useful tool for making modern phase refinement procedures more efficient.Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Burla, M.C.Carrozzini, B.Cascarano, G.L.Giacovazzo, C.Polidori, G.2017-09-13doi:10.1107/S2053273317011585International Union of CrystallographyThe most popular difference syntheses are characterized and a new difference synthesis is proposed.ENphasingdifference Fourier synthesesjoint probability distribution functionsDifference electron densities do not play a central role in modern phase refinement approaches, essentially because of the explosive success of the EDM (electron-density modification) techniques, mainly based on observed electron-density syntheses. Difference densities however have been recently rediscovered in connection with the VLD (Vive la Difference) approach, because they are a strong support for strengthening EDM approaches and for ab initio crystal structure solution. In this paper the properties of the most documented difference electron densities, here denoted as F − Fp, mF − Fp and mF − DFp syntheses, are studied. In addition, a fourth new difference synthesis, here denoted as {\overline F_q} synthesis, is proposed. It comes from the study of the same joint probability distribution function from which the VLD approach arose. The properties of the {\overline F_q} syntheses are studied and compared with those of the other three syntheses. The results suggest that the {\overline F_q} difference may be a useful tool for making modern phase refinement procedures more efficient.text/htmlAbout difference electron densities and their propertiestext6732017-09-13Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Aresearch papers00The Rome de Lisle problem
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The `Rome de Lisle problem' on the vertex and edge truncations has been formulated and solved for all crystal closed simple forms (two, eight, five and 15 for orthorhombic, trigonal + hexagonal, tetragonal and cubic syngonies, respectively). The collections of simple forms obtained are enumerated and considered as special combinations of simple forms in symmetry classes.Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Voytekhovsky, Y.L.Stepenshchikov, D.G.2017-09-13doi:10.1107/S2053273317011834International Union of CrystallographyThe vertex and edge truncations of all crystal closed simple forms are enumerated and interpreted as special combinations of crystal simple forms.ENcrystal closed simple formssymmetry classesvertex and edge truncationsRome de Lisle problemcrystalline polyhedraThe `Rome de Lisle problem' on the vertex and edge truncations has been formulated and solved for all crystal closed simple forms (two, eight, five and 15 for orthorhombic, trigonal + hexagonal, tetragonal and cubic syngonies, respectively). The collections of simple forms obtained are enumerated and considered as special combinations of simple forms in symmetry classes.text/htmlThe Rome de Lisle problemtext6732017-09-13Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Ashort communications00