International
Tables for
Crystallography
Volume B
Reciprocal space
Edited by U. Shmueli

International Tables for Crystallography (2006). Vol. B. ch. 2.1, p. 196   | 1 | 2 |

## Section 2.1.5.2. Ideal centric distributions

U. Shmuelia* and A. J. C. Wilsonb

aSchool of Chemistry, Tel Aviv University, Tel Aviv 69 978, Israel, and bSt John's College, Cambridge, England
Correspondence e-mail:  ushmueli@post.tau.ac.il

#### 2.1.5.2. Ideal centric distributions

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When a non-dispersive crystal is centrosymmetric, and the space-group origin is chosen at a crystallographic centre of symmetry, the imaginary part B of its structure amplitude is zero. In the simplest case, space group , the contribution of the jth atom plus its centrosymmetric counterpart is . The calculation of goes through as before, with allowance for the fact that there are pairs instead of N independent atoms, giving or equivalently or