Single-wavelength anomalous dispersion

Single-wavelength anomalous dispersion (SAD) is a technique used in X-ray crystallography to solve the phase problem, which is crucial for determining the three-dimensional structures of macromolecules, such as proteins and nucleic acids. The phase problem arises because X-ray diffraction data only provide the amplitudes of the diffracted waves, but not their phases, which are necessary for reconstructing the electron density map.