Crystallographic structure refinement

Transferred electron density fragments obtained by AFDF method can provide excellent approximations. One such approach, formulated in terms of transferability of fragment density matrices within the AFDF framework is a tool that has been suggested as an approach to macromolecular quantum chemistry [114, 115, 130, 142-146] and to a new density fitting algorithm in the crystallographic structure refinement process [161]. 

Mezey, P.G. (1998) A crystallographic structure refinement approach using ab initio quality additive fuzzy density fragments. In Advances in Molecular Structure Research, Hargittai, M. and Hargittai, I. (Eds.), JAI Press, New York. 

Optimization problems in crystallographic structure refinement are seldom convex, that is very rarely characterized by a unimodal function/(x). Regularization of a two-atom model is an example of such a unimodal function. Fig. 11.2a. in contrast. Fig. 11.2b shows a profile of a function for modelling an amino acid side chain - the peaks correspond to the possible rotamers. In this case, the shape of the function/(x) is called multimodal. Such functions arise naturally in structural macromolecular optimization problems and possess a highly complex multiminima energy landscape that does not lend itself favourably to standard robust optimization techniques. 

Rice, L.M. and Brunger, A.T. (1994) Torsion angle dynamics reduced variable conformational sampling enhances crystallographic structure refinement. Proteins 19,277-290. 

Freer, S. T., Alden, R. A., Carter, C. W., Jr., and Kraut, J. (1975). Crystallographic structure refinement of Chromatium high potential iron protein at two angstroms resolution. /. Biol. Chem. 250, 46-54. 

Dynamics Reduced Variable Conformational Sampling Enhances Crystallographic Structure Refinement. 

Chapter 12. Simulated annealing applied to crystallographic structure refinement... 

Brunger, A.T. and Rice, L.M. (1995) Simulated Annealing Applied in Crystallographic Structure Refinement, in Adaption of Simulated Annealing to Chemical Optimization Problems (ed. J. H. Kalivas) Elsevier, Amsterdam, p. 259. 

A CRYSTALLOGRAPHIC STRUCTURE REFINEMENT APPROACH USING AB /N/T/O QUALITY ADDITIVE, FUZZY DENSITY FRAGMENTS... 

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... 

L. M. Rice and A. T. Briinger, Torsion angle dynamics Reduced variable conformational samphng enhances crystallographic structure refinement. Proteins 19, 277-290 (1994). 

Cq( CI), 5iso ( Cl), and 2 ( Cl) relative to the experimental values [31-33]. Such information is useful when attempting to interpret NMR data in cases where the structure is not known a priori, or where NMR crystallographic structure refinement protocols are used. 

C.M. Widdifield, D.L. Bryce, Crystallographic structure refinement with quadrupolar nuclei a combined solid-state NMR and GIPAW DFT example using MgBt2, Phys. Chem. Chem. Phys. 11 (2009) 7120-7122. 

Crystallographic structure refinement is generally understood to be the last step in the determination of a crystal structure by diffraction methods. The usual procedure of a crystal structure analysis includes collection of X-ray or neutron diffraction intensities, data reduction yielding structure factor amplitudes, the solution of the crystallographic phase problem yielding approximate structural parameters and finally refinement of these parameters to obtain a best fit of the observed structure factor amplitudes with... 

M. Body, G. SiUy, C. Legein, J.-Y. Buzare, F. Calvayrac, P. Blaha, Al NMR experiments and quadrupolar parameter ab initio calculations crystallographic structure refinement of P-BajAlFs, Chem. Phys. Lett., 424, 321 326 (2006). 

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