Breakdown of Friedel law in the presence of  anomalous dispersion by an atom or group of atoms in a molecule. The non-anomalous contribution to the structure factor by those atoms is FH. FP is the contribution from the rest of the atoms and FPH is the sum. In the absence of absorption (fA ~ 0) the amplitude of the Friedel pairs FPH and FPH- is the approximately the same. When fA is significant, it introduces a difference in the amplitude of the total structure factor F and its Friedel mate F-
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