Breaking Friedel's Law

Friedel pairs

Friedel pairs are Bragg reflections related by inversion through the origin.

Friedel's Law

Friedel's Law states that members of a Friedel pair have equal amplitude and opposite phase.

Anomalous Scattering breaks the law

Friedel's Law is broken whenever there is anomalous scattering. If all atoms scatter equally, then the amplitudes remain equal but the phase relationship no longer holds. This is because the f'' term is always positive.
If some atoms scatter anomalously and some don't, then both the amplitude and phase relationships are broken.

back to X-ray Anomalous Scattering Bijvoet Pairs
Ethan A Merritt ©1996-2001/ / Biomolecular Structure Center at UW