Crystal Structure Refinement
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Crystal Structure Refinement
Crystal Structure Refinement is a mixture of textbook and tutorial. As A Crystallographers Guide to SHELXL it covers advanced aspects of practical crystal structure refinement, which have not been much addressed by textbooks so far. After an introduction to SHELXL in the first chapter, a brief survey of crystal structure refinement is provided. Chapters three and higher address the various aspects of structure refinement, from the treatment of hydrogen atoms to the assignment of atom types, to disorder, to non-crystallographic symmetry and twinning. One chapter is dedicated to the refinement of macromolecular structures and two short chapters deal with structure validation (one for small molecule structures and one for macromolecules). In each of the chapters the book gives refinement examples, based on the program SHELXL, describing every problem in detail. It comes with a CD-ROM with all files necessary to reproduce the refinements.
Structural refinement of single crystals using digital-large angle convergent beam electron diffraction
We explore the capability of digital-large angle convergent beam electron diffraction (D-LACBED) data for the structural refinement of single crystals. To achieve this, we use three materials as test cases. We use corundum for atomic position refi nement, copper and gallium arsenide for Debye-Waller factor (DWF) re finement. D-LACBED patterns are found to be extremely sensitive to atomic position, within 0.4 pm of reference X-ray values. The patterns are less sensitive to DWF (using the independent atom model - IAM) but nonetheless give good agreement to X-ray and Mossbauer radiation values for copper. We find the IAM to be insufficient for accurate refinement of gallium arsenide due to the influence of previously suggested strong anharmonicity and bonding within the material. Finally, we use simulation to explore the sensitivity of D-LACBED patterns through most re fineable structural parameters, providing context to the aforementioned results. During the analysis we see that higher g-vector patterns within the D-LACBED data may be more sensitive to structural parameters in general.