Accurate methods for crystal structure determination using aspects of dynamical diffraction theory

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An approach to the solution of crystal structures has been developed over the past ten years which is based on the intensities of high order Laue zone (HOLZ) fine structure lines present in zone axis patterns. It is a common observation that when the individual reflections in a HOLZ ring are studied in detail, several individual excess lines are observed. These individual lines are directly related to the excited branches of the dispersion surface, created by the two dimensional dynamical diffraction which occurs in the zero order Laue zone (ZOLZ). They may either directly correspond to a single branch of the dispersion surface (a unique Bloch state) or else to a cluster of close branches (a small number of distinct Bloch states). It is often the case that the intensities of these lines may be derived from a pseudo-kinematical theory, which greatly simplifies the process of deducing atomic positions from the experimental data.