Space group

The space group of hexagonal H₂O ice is P6₃/mmc. The first m indicates the mirror plane perpendicular to the c-axis (a), the second m indicates the mirror planes parallel to the c-axis (b), and the c indicates the glide planes (b) and (c). The black boxes outline the unit cell.

In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions.<ref>Template:Cite journal</ref> The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that leave it unchanged. In three dimensions, space groups are classified into 219 distinct types, or 230 types if chiral copies are considered distinct. Space groups are discrete cocompact groups of isometries of an oriented Euclidean space in any number of dimensions. In dimensions other than 3, they are sometimes called Bieberbach groups.

In crystallography, space groups are also called the crystallographic or Fedorov groups, and represent a description of the symmetry of the crystal. A definitive source regarding 3-dimensional space groups is the International Tables for Crystallography Template:Harvtxt.

HistoryEdit

Space groups in 2 dimensions are the 17 wallpaper groups which have been known for several centuries, though the proof that the list was complete was only given in 1891, after the much more difficult classification of space groups had largely been completed.Template:Sfnp

In 1879 the German mathematician Leonhard Sohncke listed the 65 space groups (called Sohncke groups) whose elements preserve the chirality.<ref>Template:Cite book</ref> More accurately, he listed 66 groups, but both the Russian mathematician and crystallographer Evgraf Fedorov and the German mathematician Arthur Moritz Schoenflies noticed that two of them were really the same. The space groups in three dimensions were first enumerated in 1891 by FedorovTemplate:Sfnp (whose list had two omissions (ITemplate:Overline3d and Fdd2) and one duplication (Fmm2)), and shortly afterwards in 1891 were independently enumerated by Schönflies<ref>Template:Cite book</ref> (whose list had four omissions (ITemplate:Overline3d, Pc, Cc, ?) and one duplication (PTemplate:Overline2₁m)). The correct list of 230 space groups was found by 1892 during correspondence between Fedorov and Schönflies.<ref>Template:Cite journal</ref> Template:Harvs later enumerated the groups with a different method, but omitted four groups (Fdd2, ITemplate:Overline2d, PTemplate:Overline2₁d, and PTemplate:Overline2₁c) even though he already had the correct list of 230 groups from Fedorov and Schönflies; the common claim that Barlow was unaware of their work is incorrect.Template:Citation needed Template:Harvtxt describes the history of the discovery of the space groups in detail.

ElementsEdit

The space groups in three dimensions are made from combinations of the 32 crystallographic point groups with the 14 Bravais lattices, each of the latter belonging to one of 7 lattice systems. What this means is that the action of any element of a given space group can be expressed as the action of an element of the appropriate point group followed optionally by a translation. A space group is thus some combination of the translational symmetry of a unit cell (including lattice centering), the point group symmetry operations of reflection, rotation and improper rotation (also called rotoinversion), and the screw axis and glide plane symmetry operations. The combination of all these symmetry operations results in a total of 230 different space groups describing all possible crystal symmetries.

The number of replicates of the asymmetric unit in a unit cell is thus the number of lattice points in the cell times the order of the point group. This ranges from 1 in the case of space group P1 to 192 for a space group like FmTemplate:Overlinem, the NaCl structure.

Elements fixing a pointEdit

The elements of the space group fixing a point of space are the identity element, reflections, rotations and improper rotations, including inversion points.

TranslationsEdit

The translations form a normal abelian subgroup of rank 3, called the Bravais lattice (so named after French physicist Auguste Bravais). There are 14 possible types of Bravais lattice. The quotient of the space group by the Bravais lattice is a finite group which is one of the 32 possible point groups.

Glide planesEdit

A glide plane is a reflection in a plane, followed by a translation parallel with that plane. This is noted by <math>a</math>, <math>b</math>, or <math>c</math>, depending on which axis the glide is along. There is also the <math>n</math> glide, which is a glide along the half of a diagonal of a face, and the <math>d</math> glide, which is a fourth of the way along either a face or space diagonal of the unit cell. The latter is called the diamond glide plane as it features in the diamond structure. In 17 space groups, due to the centering of the cell, the glides occur in two perpendicular directions simultaneously, i.e. the same glide plane can be called b or c, a or b, a or c. For example, group Abm2 could be also called Acm2, group Ccca could be called Cccb. In 1992, it was suggested to use symbol e for such planes. The symbols for five space groups have been modified:

Space group no.	39	41	64	67	68
New symbol	Aem2	Aea2	Cmce	Cmme	Ccce
Old Symbol	Abm2	Aba2	Cmca	Cmma	Ccca

Screw axesEdit

A screw axis is a rotation about an axis, followed by a translation along the direction of the axis. These are noted by a number, n, to describe the degree of rotation, where the number is how many operations must be applied to complete a full rotation (e.g., 3 would mean a rotation one third of the way around the axis each time). The degree of translation is then added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. So, 2₁ is a twofold rotation followed by a translation of 1/2 of the lattice vector.

General formulaEdit

The general formula for the action of an element of a space group is

y = M.x + D

where M is its matrix, D is its vector, and where the element transforms point x into point y. In general, D = D (lattice) + Template:Not a typo, where Template:Not a typo is a unique function of M that is zero for M being the identity. The matrices M form a point group that is a basis of the space group; the lattice must be symmetric under that point group, but the crystal structure itself may not be symmetric under that point group as applied to any particular point (that is, without a translation). For example, the diamond cubic structure does not have any point where the cubic point group applies.

The lattice dimension can be less than the overall dimension, resulting in a "subperiodic" space group. For (overall dimension, lattice dimension):

(1,1): One-dimensional line groups
(2,1): Two-dimensional line groups: frieze groups
(2,2): Wallpaper groups
(3,1): Three-dimensional line groups; with the 3D crystallographic point groups, the rod groups
(3,2): Layer groups
(3,3): The space groups discussed in this article

ChiralityEdit

The 65 "Sohncke" space groups, not containing any mirrors, inversion points, improper rotations or glide planes, yield chiral crystals, not identical to their mirror image; whereas space groups that do include at least one of those give achiral crystals. Achiral molecules sometimes form chiral crystals, but chiral molecules always form chiral crystals, in one of the space groups that permit this.

Among the 65 Sohncke groups are 22 that come in 11 enantiomorphic pairs.

CombinationsEdit

Only certain combinations of symmetry elements are possible in a space group. Translations are always present, and the space group P1 has only translations and the identity element. The presence of mirrors implies glide planes as well, and the presence of rotation axes implies screw axes as well, but the converses are not true. An inversion and a mirror implies two-fold screw axes, and so on.

NotationEdit

Template:Further There are at least ten methods of naming space groups. Some of these methods can assign several different names to the same space group, so altogether there are many thousands of different names.

Number: The International Union of Crystallography publishes tables of all space group types, and assigns each a unique number from 1 to 230. The numbering is arbitrary, except that groups with the same crystal system or point group are given consecutive numbers.

Template:Term Template:Term Template:Defn

Hall notation<ref>{{#invoke: citation/CS1|citation

|CitationClass=web }}</ref>

Space group notation with an explicit origin. Rotation, translation and axis-direction symbols are clearly separated and inversion centers are explicitly defined. The construction and format of the notation make it particularly suited to computer generation of symmetry information. For example, group number 3 has three Hall symbols: P 2y (P 1 2 1), P 2 (P 1 1 2), P 2x (P 2 1 1).
Schönflies notation: The space groups with given point group are numbered by 1, 2, 3, ... (in the same order as their international number) and this number is added as a superscript to the Schönflies symbol for the point group. For example, groups numbers 3 to 5 whose point group is C₂ have Schönflies symbols CTemplate:Sup sub, CTemplate:Sup sub, CTemplate:Sup sub.

Template:Term Template:Term Template:Term Template:Defn Template:Term Template:Term Template:Defn

Coxeter notation: Spatial and point symmetry groups, represented as modifications of the pure reflectional Coxeter groups.
Geometric notation<ref>Template:Cite journal</ref>: A geometric algebra notation.

Classification systemsEdit

There are (at least) 10 different ways to classify space groups into classes. The relations between some of these are described in the following table. Each classification system is a refinement of the ones below it. To understand an explanation given here it may be necessary to understand the next one down.

(Crystallographic) space group types (230 in three dimensions)
Two space groups, considered as subgroups of the group of affine transformations of space, have the same space group type if they are the same up to an affine transformation of space that preserves orientation. Thus e.g. a change of angle between translation vectors does not affect the space group type if it does not add or remove any symmetry. A more formal definition involves conjugacy (see Symmetry group). In three dimensions, for 11 of the affine space groups, there is no chirality-preserving (i.e. orientation-preserving) map from the group to its mirror image, so if one distinguishes groups from their mirror images, these each split into two cases (such as P4₁ and P4₃). So, instead of the 54 affine space groups that preserve chirality, there are 54 + 11 = 65 space group types that preserve chirality (the Sohncke groups). For most chiral crystals, the two enantiomorphs belong to the same crystallographic space group, such as P2₁3 for FeSi,<ref>Template:Cite journal</ref> but for others, such as quartz, they belong to two enantiomorphic space groups.
Affine space group types (219 in three dimensions)
Two space groups, considered as subgroups of the group of affine transformations of space, have the same affine space group type if they are the same up to an affine transformation, even if that inverts orientation. The affine space group type is determined by the underlying abstract group of the space group. In three dimensions, Fifty-four of the affine space group types preserve chirality and give chiral crystals. The two enantiomorphs of a chiral crystal have the same affine space group.
Arithmetic crystal classes (73 in three dimensions)
Sometimes called Z-classes. These are determined by the point group together with the action of the point group on the subgroup of translations. In other words, the arithmetic crystal classes correspond to conjugacy classes of finite subgroup of the general linear group GL_n(Z) over the integers. A space group is called symmorphic (or split) if there is a point such that all symmetries are the product of a symmetry fixing this point and a translation. Equivalently, a space group is symmorphic if it is a semidirect product of its point group with its translation subgroup. There are 73 symmorphic space groups, with exactly one in each arithmetic crystal class. There are also 157 nonsymmorphic space group types with varying numbers in the arithmetic crystal classes. Arithmetic crystal classes may be interpreted as different orientations of the point groups in the lattice, with the group elements' matrix components being constrained to have integer coefficients in lattice space. This is rather easy to picture in the two-dimensional, wallpaper group case. Some of the point groups have reflections, and the reflection lines can be along the lattice directions, halfway in between them, or both. None: C₁: p1; C₂: p2; C₃: p3; C₄: p4; C₆: p6 Along: D₁: pm, pg; D₂: pmm, pmg, pgg; D₃: p31m Between: D₁: cm; D₂: cmm; D₃: p3m1 Both: D₄: p4m, p4g; D₆: p6m
(geometric) Crystal classes (32 in three dimensions)	Bravais flocks (14 in three dimensions)
Sometimes called Q-classes. The crystal class of a space group is determined by its point group: the quotient by the subgroup of translations, acting on the lattice. Two space groups are in the same crystal class if and only if their point groups, which are subgroups of GL_n(Z), are conjugate in the larger group GL_n(Q).	These are determined by the underlying Bravais lattice type. These correspond to conjugacy classes of lattice point groups in GL_n(Z), where the lattice point group is the group of symmetries of the underlying lattice that fix a point of the lattice, and contains the point group.
Crystal systems (7 in three dimensions)	Lattice systems (7 in three dimensions)
Crystal systems are an ad hoc modification of the lattice systems to make them compatible with the classification according to point groups. They differ from crystal families in that the hexagonal crystal family is split into two subsets, called the trigonal and hexagonal crystal systems. The trigonal crystal system is larger than the rhombohedral lattice system, the hexagonal crystal system is smaller than the hexagonal lattice system, and the remaining crystal systems and lattice systems are the same.	The lattice system of a space group is determined by the conjugacy class of the lattice point group (a subgroup of GL_n(Z)) in the larger group GL_n(Q). In three dimensions the lattice point group can have one of the 7 different orders 2, 4, 8, 12, 16, 24, or 48. The hexagonal crystal family is split into two subsets, called the rhombohedral and hexagonal lattice systems.
Crystal families (6 in three dimensions)
The point group of a space group does not quite determine its lattice system, because occasionally two space groups with the same point group may be in different lattice systems. Crystal families are formed from lattice systems by merging the two lattice systems whenever this happens, so that the crystal family of a space group is determined by either its lattice system or its point group. In 3 dimensions the only two lattice families that get merged in this way are the hexagonal and rhombohedral lattice systems, which are combined into the hexagonal crystal family. The 6 crystal families in 3 dimensions are called triclinic, monoclinic, orthorhombic, tetragonal, hexagonal, and cubic. Crystal families are commonly used in popular books on crystals, where they are sometimes called crystal systems.

Template:Harvs gave another classification of the space groups, called a fibrifold notation, according to the fibrifold structures on the corresponding orbifold. They divided the 219 affine space groups into reducible and irreducible groups. The reducible groups fall into 17 classes corresponding to the 17 wallpaper groups, and the remaining 35 irreducible groups are the same as the cubic groups and are classified separately.

In other dimensionsEdit

Bieberbach's theoremsEdit

In n dimensions, an affine space group, or Bieberbach group, is a discrete subgroup of isometries of n-dimensional Euclidean space with a compact fundamental domain. Template:Harvs proved that the subgroup of translations of any such group contains n linearly independent translations, and is a free abelian subgroup of finite index, and is also the unique maximal normal abelian subgroup. He also showed that in any dimension n there are only a finite number of possibilities for the isomorphism class of the underlying group of a space group, and moreover the action of the group on Euclidean space is unique up to conjugation by affine transformations. This answers part of Hilbert's eighteenth problem. Template:Harvtxt showed that conversely any group that is the extensionTemplate:Definition of Zⁿ by a finite group acting faithfully is an affine space group. Combining these results shows that classifying space groups in n dimensions up to conjugation by affine transformations is essentially the same as classifying isomorphism classes for groups that are extensions of Zⁿ by a finite group acting faithfully.

It is essential in Bieberbach's theorems to assume that the group acts as isometries; the theorems do not generalize to discrete cocompact groups of affine transformations of Euclidean space. A counter-example is given by the 3-dimensional Heisenberg group of the integers acting by translations on the Heisenberg group of the reals, identified with 3-dimensional Euclidean space. This is a discrete cocompact group of affine transformations of space, but does not contain a subgroup Z³.

Classification in small dimensionsEdit

This table gives the number of space group types in small dimensions, including the numbers of various classes of space group. The numbers of enantiomorphic pairs are given in parentheses.

Dimensions	Crystal families, Template:OEIS el	Crystal systems, Template:OEIS el	Bravais lattices, Template:OEIS el	Abstract crystallographic point groups, Template:OEIS el	Geometric crystal classes, Q-classes, crystallographic point groups, Template:OEIS el	Arithmetic crystal classes, Z-classes, Template:OEIS el	Affine space group types, Template:OEIS el	Crystallographic space group types, Template:OEIS el
0Template:Efn	1	1	1	1	1	1	1	1
1Template:Efn	1	1	1	2	2	2	2	2
2Template:Efn	4	4	5	9	10	13	17	17
3Template:Efn	6	7	14	18	32	73	219 (+11)	230
4Template:Efn	23 (+6)	33 (+7)	64 (+10)	118	227 (+44)	710 (+70)	4783 (+111)	4894
5Template:Efn	32	59	189	239	955	6079	222018 (+79)	222097
6Template:Efn	91	251	841	1594	7103	85308 (+?)	28927915 (+?)	?

Template:Noteslist

Magnetic groups and time reversalEdit

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}

In addition to crystallographic space groups there are also magnetic space groups (also called two-color (black and white) crystallographic groups or Shubnikov groups). These symmetries contain an element known as time reversal. They treat time as an additional dimension, and the group elements can include time reversal as reflection in it. They are of importance in magnetic structures that contain ordered unpaired spins, i.e. ferro-, ferri- or antiferromagnetic structures as studied by neutron diffraction. The time reversal element flips a magnetic spin while leaving all other structure the same and it can be combined with a number of other symmetry elements. Including time reversal there are 1651 magnetic space groups in 3D Template:Harv. It has also been possible to construct magnetic versions for other overall and lattice dimensions (Daniel Litvin's papers, Template:Harv, Template:Harv). Frieze groups are magnetic 1D line groups and layer groups are magnetic wallpaper groups, and the axial 3D point groups are magnetic 2D point groups. Number of original and magnetic groups by (overall, lattice) dimension:Template:Harv Template:Harv

Overall dimension	Lattice dimension	Ordinary groups			Magnetic groups
Overall dimension	Lattice dimension	Name	Symbol	Count	Symbol	Count
0	0	Zero-dimensional symmetry group	<math>G_0</math>	1	<math>G_0^1</math>	2
1	0	One-dimensional point groups	<math>G_{10}</math>	2	<math>G_{10}^1</math>	5
1	1	One-dimensional discrete symmetry groups	<math>G_1</math>	2	<math>G_1^1</math>	7
2	0	Two-dimensional point groups	<math>G_{20}</math>	10	<math>G_{20}^1</math>	31
	1	Frieze groups	<math>G_{21}</math>	7	<math>G_{21}^1</math>	31
	2	Wallpaper groups	<math>G_2</math>	17	<math>G_2^1</math>	80
3	0	Three-dimensional point groups	<math>G_{30}</math>	32	<math>G_{30}^1</math>	122
	1	Rod groups	<math>G_{31}</math>	75	<math>G_{31}^1</math>	394
	2	Layer groups	<math>G_{32}</math>	80	<math>G_{32}^1</math>	528
	3	Three-dimensional space groups	<math>G_{3}</math>	230	<math>G_{3}^1</math>	1651
4	0	Four-dimensional point groups	<math>G_{40}</math>	271	<math>G_{40}^1</math>	1202
	1		<math>G_{41}</math>	343
	2		<math>G_{42}</math>	1091
	3		<math>G_{43}</math>	1594
	4	Four-dimensional discrete symmetry groups	<math>G_{4}</math>	4894	<math>G_{4}^1</math>	62227

Table of space groups in 2 dimensions (wallpaper groups)Edit

Table of the wallpaper groups using the classification of the 2-dimensional space groups:

Crystal system, Bravais lattice	Geometric class, point group					Arithmetic class	Wallpaper groups (cell diagram)
Crystal system, Bravais lattice	Int'l	Schön.	Orbifold	Cox.	Ord.	Arithmetic class	Wallpaper groups (cell diagram)
Oblique File:2d mp.svg	1	C₁	(1)	[ ]⁺	1	None	p1 (1)	File:Wallpaper group diagram p1.svg
Oblique File:2d mp.svg	2	C₂	(22)	[2]⁺	2	None	p2 (2222)	File:Wallpaper group diagram p2.svg
Rectangular File:2d op rectangular.svg	m	D₁	(*)	[ ]	2	Along	pm (**)	File:Wallpaper group diagram pm.svg	pg (××)	File:Wallpaper group diagram pg.svg
Rectangular File:2d op rectangular.svg	2mm	D₂	(*22)	[2]	4	Along	pmm (*2222)	File:Wallpaper group diagram pmm.svg	pmg (22*)	File:Wallpaper group diagram pmg.svg
Centered rectangular File:2d oc rectangular.svg	m	D₁	(*)	[ ]	2	Between	cm (*×)	File:Wallpaper group diagram cm.svg
Centered rectangular File:2d oc rectangular.svg	2mm	D₂	(*22)	[2]	4	Between	cmm (2*22)	File:Wallpaper group diagram cmm.svg	pgg (22×)	File:Wallpaper group diagram pgg.svg
Square File:2d tp.svg	4	C₄	(44)	[4]⁺	4	None	p4 (442)	File:Wallpaper group diagram p4 square.svg
Square File:2d tp.svg	4mm	D₄	(*44)	[4]	8	Both	p4m (*442)	File:Wallpaper group diagram p4m square.svg	p4g (4*2)	File:Wallpaper group diagram p4g square.svg
Hexagonal File:2d hp.svg	3	C₃	(33)	[3]⁺	3	None	p3 (333)	File:Wallpaper group diagram p3.svg
	3m	D₃	(*33)	[3]	6	Between	p3m1 (*333)	File:Wallpaper group diagram p3m1.svg	p31m (3*3)	File:Wallpaper group diagram p31m.svg
	6	C₆	(66)	[6]⁺	6	None	p6 (632)	File:Wallpaper group diagram p6.svg
	6mm	D₆	(*66)	[6]	12	Both	p6m (*632)	File:Wallpaper group diagram p6m.svg

For each geometric class, the possible arithmetic classes are

None: no reflection lines
Along: reflection lines along lattice directions
Between: reflection lines halfway in between lattice directions
Both: reflection lines both along and between lattice directions

Table of space groups in 3 dimensionsEdit

Template:Further

[[Space group#Notation\|Template:Abbr]]	Crystal system, (count), Bravais lattice	Point group					Space groups (international short symbol)
[[Space group#Notation\|Template:Abbr]]	Crystal system, (count), Bravais lattice	Int'l	Schön.	Orbifold	Cox.	Ord.	Space groups (international short symbol)
1	Triclinic (2) File:Triclinic.svg	1	C₁	11	[ ]⁺	1	P1
2	Triclinic (2) File:Triclinic.svg	Template:Overline	C_i	1×	[2⁺,2⁺]	2	PTemplate:Overline
3–5	Monoclinic (13) File:Monoclinic.svg File:Base-centered monoclinic.svg	2	C₂	22	[2]⁺	2	P2, P2₁ C2
6–9		m	C_s	*11	[ ]	2	Pm, Pc Cm, Cc
10–15		2/m	C_2h	2*	[2,2⁺]	4	P2/m, P2₁/m C2/m, P2/c, P2₁/c C2/c
16–24	Orthorhombic (59) File:Orthorhombic.svg File:Orthorhombic-body-centered.svg File:Orthorhombic-base-centered.svg File:Orthorhombic-face-centered.svg	222	D₂	222	[2,2]⁺	4	P222, P222₁, P2₁2₁2, P2₁2₁2₁ C222₁, C222 F222 I222, I2₁2₁2₁
25–46		mm2	C_2v	*22	[2]	4	Pmm2, Pmc2₁, Pcc2, Pma2, Pca2₁, Pnc2, Pmn2₁, Pba2, Pna2₁, Pnn2 Cmm2, Cmc2₁, Ccc2, Amm2, Aem2, Ama2, Aea2 Fmm2, Fdd2 Imm2, Iba2, Ima2
47–74		mmm	D_2h	*222	[2,2]	8	Pmmm, Pnnn, Pccm, Pban, Pmma, Pnna, Pmna, Pcca, Pbam, Pccn, Pbcm, Pnnm, Pmmn, Pbcn, Pbca, Pnma Cmcm, Cmce, Cmmm, Cccm, Cmme, Ccce Fmmm, Fddd Immm, Ibam, Ibca, Imma
75–80	Tetragonal (68) File:Tetragonal.svg File:Tetragonal-body-centered.svg	4	C₄	44	[4]⁺	4	P4, P4₁, P4₂, P4₃, I4, I4₁
81–82		Template:Overline	S₄	2×	[2⁺,4⁺]	4	PTemplate:Overline, ITemplate:Overline
83–88		4/m	C_4h	4*	[2,4⁺]	8	P4/m, P4₂/m, P4/n, P4₂/n I4/m, I4₁/a
89–98		422	D₄	224	[2,4]⁺	8	P422, P42₁2, P4₁22, P4₁2₁2, P4₂22, P4₂2₁2, P4₃22, P4₃2₁2 I422, I4₁22
99–110		4mm	C_4v	*44	[4]	8	P4mm, P4bm, P4₂cm, P4₂nm, P4cc, P4nc, P4₂mc, P4₂bc I4mm, I4cm, I4₁md, I4₁cd
111–122		Template:Overline2m	D_2d	2*2	[2⁺,4]	8	PTemplate:Overline2m, PTemplate:Overline2c, PTemplate:Overline2₁m, PTemplate:Overline2₁c, PTemplate:Overlinem2, PTemplate:Overlinec2, PTemplate:Overlineb2, PTemplate:Overlinen2 ITemplate:Overlinem2, ITemplate:Overlinec2, ITemplate:Overline2m, ITemplate:Overline2d
123–142		4/mmm	D_4h	*224	[2,4]	16	P4/mmm, P4/mcc, P4/nbm, P4/nnc, P4/mbm, P4/mnc, P4/nmm, P4/ncc, P4₂/mmc, P4₂/mcm, P4₂/nbc, P4₂/nnm, P4₂/mbc, P4₂/mnm, P4₂/nmc, P4₂/ncm I4/mmm, I4/mcm, I4₁/amd, I4₁/acd
143–146	Trigonal (25) File:Hexagonal latticeR.svg File:Hexagonal latticeFRONT.svg	3	C₃	33	[3]⁺	3	P3, P3₁, P3₂ R3
147–148		Template:Overline	S₆	3×	[2⁺,6⁺]	6	PTemplate:Overline, RTemplate:Overline
149–155		32	D₃	223	[2,3]⁺	6	P312, P321, P3₁12, P3₁21, P3₂12, P3₂21 R32
156–161		3m	C_3v	*33	[3]	6	P3m1, P31m, P3c1, P31c R3m, R3c
162–167		Template:Overlinem	D_3d	2*3	[2⁺,6]	12	PTemplate:Overline1m, PTemplate:Overline1c, PTemplate:Overlinem1, PTemplate:Overlinec1 RTemplate:Overlinem, RTemplate:Overlinec
168–173	Hexagonal (27) File:Hexagonal latticeFRONT.svg	6	C₆	66	[6]⁺	6	P6, P6₁, P6₅, P6₂, P6₄, P6₃
174		Template:Overline	C_3h	3*	[2,3⁺]	6	PTemplate:Overline
175–176		6/m	C_6h	6*	[2,6⁺]	12	P6/m, P6₃/m
177–182		622	D₆	226	[2,6]⁺	12	P622, P6₁22, P6₅22, P6₂22, P6₄22, P6₃22
183–186		6mm	C_6v	*66	[6]	12	P6mm, P6cc, P6₃cm, P6₃mc
187–190		Template:Overlinem2	D_3h	*223	[2,3]	12	PTemplate:Overlinem2, PTemplate:Overlinec2, PTemplate:Overline2m, PTemplate:Overline2c
191–194		6/mmm	D_6h	*226	[2,6]	24	P6/mmm, P6/mcc, P6₃/mcm, P6₃/mmc
195–199	Cubic (36) File:Cubic.svg File:Cubic-body-centered.svg File:Cubic-face-centered.svg	23	T	332	[3,3]⁺	12	P23, F23, I23 P2₁3, I2₁3
200–206		mTemplate:Overline	T_h	3*2	[3⁺,4]	24	PmTemplate:Overline, PnTemplate:Overline, FmTemplate:Overline, FdTemplate:Overline, ImTemplate:Overline, PaTemplate:Overline, IaTemplate:Overline
207–214		432	O	432	[3,4]⁺	24	P432, P4₂32 F432, F4₁32 I432 P4₃32, P4₁32, I4₁32
215–220		Template:Overline3m	T_d	*332	[3,3]	24	PTemplate:Overline3m, FTemplate:Overline3m, ITemplate:Overline3m PTemplate:Overline3n, FTemplate:Overline3c, ITemplate:Overline3d
221–230		mTemplate:Overlinem	O_h	*432	[3,4]	48	PmTemplate:Overlinem, PnTemplate:Overlinen, PmTemplate:Overlinen, PnTemplate:Overlinem FmTemplate:Overlinem, FmTemplate:Overlinec, FdTemplate:Overlinem, FdTemplate:Overlinec ImTemplate:Overlinem, IaTemplate:Overlined

Note: An e plane is a double glide plane, one having glides in two different directions. They are found in seven orthorhombic, five tetragonal and five cubic space groups, all with centered lattice. The use of the symbol e became official with Template:Harvtxt.

The lattice system can be found as follows. If the crystal system is not trigonal then the lattice system is of the same type. If the crystal system is trigonal, then the lattice system is hexagonal unless the space group is one of the seven in the rhombohedral lattice system consisting of the 7 trigonal space groups in the table above whose name begins with R. (The term rhombohedral system is also sometimes used as an alternative name for the whole trigonal system.) The hexagonal lattice system is larger than the hexagonal crystal system, and consists of the hexagonal crystal system together with the 18 groups of the trigonal crystal system other than the seven whose names begin with R.

The Bravais lattice of the space group is determined by the lattice system together with the initial letter of its name, which for the non-rhombohedral groups is P, I, F, A or C, standing for the principal, body centered, face centered, A-face centered or C-face centered lattices. There are seven rhombohedral space groups, with initial letter R.

Derivation of the crystal class from the space groupEdit

Leave out the Bravais type
Convert all symmetry elements with translational components into their respective symmetry elements without translation symmetry (Glide planes are converted into simple mirror planes; Screw axes are converted into simple axes of rotation)
Axes of rotation, rotoinversion axes and mirror planes remain unchanged.

ReferencesEdit

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External linksEdit

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