The program ASSC calculates the anomalous signal

for a crystal of a given content. The calculations take into account the possibility of partial centro-symmetry (Flack, Shmueli, Acta Cryst. (2007) A63, 257-26) and are based on the generalization of formulas presented in Olczak et al. (Acta Cryst. (2003). A59, 327-334), Olczak et al. (Acta Cryst. (2007) D63, 319-327) Olczak (46 Polish Crystallographic Meeting (2004), p.16), Olczak, Sieron (49 Polish Crystallographic Meeting (2007), p.92). Structure factor corrections are based on Kissel et al. (Acta Cryst. (1995). A51, 271-288). In the calculations all atoms in the structure are treated as anomalous scatterers.

Assuming that the structure contains N atoms of Q types, the anomalous signal can be calculated from the following formula containing the sum of Q(Q-1)/2 components (pairs of different atom types):

(A', B', Q' denotes centrosymmetric part of the structure)

where A, B = 1...Q and each of the individual component can be expressed as follows:

where and are occupancy factors of the j^th atom of type A and the i^th of type B, respectively. are the numbers of atoms of type A and B, respectively,
and $\sum_{A=1}^{Q}N_A=N$.

The program reports all individual contributions to the total anomalous signal .

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