Systematic absences

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Absences systématiques (Fr). Extinciones sistemáticas (Sp).

Definition

One speaks of systematic absences or extinctions when the structure factor is zero, due either to the centring of the lattice or to the presence of glide or screw symmetry elements. Conversely, the conditions for a reflection to exist and not to be systematically absent, are called reflection conditions.

See also

reflection conditions
Sections 2.2.13 and 12.3.5 of the International Tables of Crystallography (Volume A)