Space group - クウカングン

A space group is a group formed by a set of symmetric elements of a crystal structure, and is used to express the symmetry of the atomic arrangement in a crystal. The elements of a space group are given by the translation, rotation, and inversion (including inversion and reflection), screw axis operations, and glide operations of the space lattice, and their combinations. By applying these symmetry operations to a point in a crystal, a regular structure can be created in which the crystallographically equivalent points to that point are distributed in three-dimensional space. There are 230 types of space groups in the usual sense, which are obtained by combining 32 point groups and 14 types of Bravais lattices. Since the symmetry and regular extinction rules of X-ray diffraction intensity from a single crystal are determined by the space group, conversely, it is often possible to determine the space group from the characteristics of an X-ray diffraction photograph and other factors. Knowledge of space groups is essential for studying crystal structures using diffraction methods, and is also essential for describing crystal structures. Similar groups considered in two dimensions are called plane groups or face groups, and there are 17 types in crystals. The individual space group descriptions are fully summarized in the International Tables for Crystallography , Vol. A. [See Alternative Terms] Schönfries symbols, Hermann-Morgan symbols

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

結晶構造の対称要素の集合によってつくられる群を空間群といい，結晶中の原子配列の対称性を表すのに用いられる．空間群の要素は，空間格子の並進，回転，回反(反転・鏡映を含む)，らせん軸の操作および映進とこれらの組合せで与えられる．これらの対称操作を結晶内の1点にほどこすことにより，その点と結晶学的同価な点が，三次元空間内に分布した規則構造をつくることができる．通常の意味の空間群は230種類あり，32の点群と14種類のブラベ格子の組合せによって得られる．単結晶によるX線回折強度の対称性と規則的な消滅則は空間群で決められるので，逆にX線回折写真の特徴そのほかから空間群を決定できる場合が多い．空間群の知識は回折法により結晶構造を研究するうえで不可欠であり，また結晶構造の記載にも必須のものである．なお，二次元中で考えた同様の群を平面群または面群とよび，結晶では17種類ある．個々の空間群の説明はInternational Tables for Crystallography，Vol.Aに完全な形でまとめられている．[別用語参照]シェーンフリースの記号，ヘルマン-モーガンの記号

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