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MIN12FAL_03_Internal Symmetry_Space Groups_Handout

International international tables for x ray

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Unformatted text preview: oordinates coordinates x = X/a y = Y /b z = Z /c equivalent positions (points) general positions – a set of equivalent positions with point (site) symmetry 1. special positions – a set of equivalent positions with point (site) symmetry set higher than 1. general equivalent positions special equivalent positions International International Tables for X-ray Crystallography 1. Shortened symbol Sh 2. Schoenflies symbol 3. Crystal class 4. Crystal system 5. Space group number 6. Hermann-Mauguin symbol Hermann7. Patterson symmetry - symmetry of the Patterson function used symmetry of the Patterson function used in xin x-ray crystal structure determination. 8. Space group drawings Repeat pattern of the motifs comma different handedness comma different handedness signs signs positions above or below the plane of the page. Pattern of symmetry elements 9. Origin Origin 10. Asymmetric unit - a unique volume of the unit cell, from which the rest of the cell may be obtained operation of the symmetry elements. Vasym. unit = Vunit cell / multiplicity of the general position Zircon Space group 141 I 41/a 2/m 2/d Positions Positions Multiplicity – the number of equivalent positions in the unit cell is called th equ th the the multiplicity of a position. Wyckoff letter - R. W. G. Wyckoff’s notation Site symmetry (point symmetry) Coordinates - fractional coordinates X/a, Y/b, Z/c Please notice the lattice type. type....
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