Crystallographic structure refinement group

The crystallographic structure refinement approach suggested is based on the viability of a fuzzy and additive density fragmentation technique. Ultimately, the fundamental quantum mechanical properties of density functionals justify the fuzzy fragmentation procedure, and the very same fundamental properties also suggest new approaches to local electron density shape analysis. These possibilities have relevance both to crystallographic structure refinement as well as to a density-based interpretation of the chemical properties of functional groups and other local... 

Data analysis procedures have developed substantially over the last few years. In particular, use of least square refinement methods have been developed. Recent progress with theoretical development for the treatment of multiple scattering has resulted in Ugand group refinement such as an imidazole. We can expect further development in this area which ought to lead us to restrained least square refinement procedures for EXAFS data analysis. This type of restrained refinement is commonly used for macromolecular crystallographic structure determination where a similar problem of imderdeterminancy exists... 

In (CgHg ) P-Au-Mn(CO)g there is an approximately linear bond system P-Au-Mn, This is the normal stereochemical form that would be expected for an Au(I) atom forming two bonds. Considerable difficultly arose in the structure determination. The crystal is non-centrosymmetric and, as a further complication, contains two crystallographically different molecules with a pseudosymmetry of the heavy atom positions higher than that of the space-group. In this situation the common methods of crystal structure refinement are severely hampered. Nevertheless all atoms have been located. The distance Au-P may be used to get, by difference, a covalent radius applicable to the gold atom and hence, from the Au-Mn distance, a radius for Mn is found, A more suitable compound is the variant... 

H.M. Rietveld developed a practical method to analyze powder diffraction data. The Rietveld refinement method [6] is based on modeling a diffraction pattern according to structural information available for the phases previously identified in the pattern. This model is calculated by computer software after introduction of some crystallographic data space group symmetry, atomic species and positions within the cell, occupancies, lattice parameters, line broadening parameters, and experimental conditions. The term refinement refers to the cyclic improvement process used in the estimation of the set of parameters that can model the diffraction pattern as close as possible to the observed pattern. Usually, the Rietveld refinement is accomplished by minimizing the sum of the differences of calculated and observed intensities for each angular step of the diffraction pattern and by a... 

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