A crystallizes in space group

There are occasionally more subtle traps. Some arise out of faulty reasoning and are thus, in principle, entirely avoidable. If, for example, a crystal is found to contain a number of molecules equal to the multiplicity of the general position for its space group, that does not necessarily mean that the molecules must be on general positions. Consider the simplest possible case, a crystal in space group PI with two molecules in the unit cell. While in most instances there are two equivalent molecules on the twofold general position, cases are also known in which each molecule resides on a different center of inversion. In every such case this is a logical possibility and only an actual structure solution can rule it in or out. 

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See also in sourсe #XX -- [ , , ]

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