Bruker

About: Bruker is a company organization based out in Billerica, Massachusetts, United States. It is known for research contribution in the topics: Mass spectrometry & Detector. The organization has 555 authors who have published 1041 publications receiving 26639 citations.

The anatomy of a comprehensive constrained, restrained refinement program for the modern computing environment – Olex2 dissected

Abstract: This paper describes the mathematical basis for olex2.refine, the new refinement engine which is integrated within the Olex2 program. Precise and clear equations are provided for every computation performed by this engine, including structure factors and their derivatives, constraints, restraints and twinning; a general overview is also given of the different components of the engine and their relation to each other. A framework for adding multiple general constraints with dependencies on common physical parameters is described. Several new restraints on atomic displacement parameters are also presented.

Determination of absolute structure using Bayesian statistics on Bijvoet differences.

Abstract: A new probabilistic approach is introduced for the determination of the absolute structure of a compound which is known to be enantiopure based on Bijvoet-pair intensity differences. The new method provides relative probabilities for different models of the chiral composition of the structure. The outcome of this type of analysis can also be cast in the form of a new value, along with associated standard uncertainty, that resembles the value of the well known Flack x parameter. The standard uncertainty we obtain is often about half of the standard uncertainty in the value of the Flack x parameter. The proposed formalism is suited in particular to absolute configuration determination from diffraction data of biologically active (pharmaceutical) compounds where the strongest resonant scattering signal often comes from oxygen. It is shown that a reliable absolute configuration assignment in such cases can be made on the basis of Cu Kα data, and in some cases even with carefully measured Mo Kα data.

Indexing of powder diffraction patterns by iterative use of singular value decomposition

Abstract: A fast method for indexing powder diffraction patterns has been developed for large and small lattices of all symmetries. The method is relatively insensitive to impurity peaks and missing high d-spacings: on simulated data, little effect in terms of successful indexing has been observed when one in three d-spacings are randomly removed. Comparison with three of the most popular indexing programs, namely ITO, DICVOL91 and TREOR90, has shown that the present method as implemented in the program TOPAS is more successful at indexing simulated data. Also significant is that the present method performs well on typically noisy data with large diffractometer zero errors. Critical to its success, the present method uses singular value decomposition in an iterative manner for solving linear equations relating hkl values to d-spacings.

Fundamental Parameters Line Profile Fitting in Laboratory Diffractometers.

Abstract: The fundamental parameters approach to line profile fitting uses physically based models to generate the line profile shapes Fundamental parameters profile fitting (FPPF) has been used to synthesize and fit data from both parallel beam and divergent beam diffractometers The refined parameters are determined by the diffractometer configuration In a divergent beam diffractometer these include the angular aperture of the divergence slit, the width and axial length of the receiving slit, the angular apertures of the axial Soller slits, the length and projected width of the x-ray source, the absorption coefficient and axial length of the sample In a parallel beam system the principal parameters are the angular aperture of the equatorial analyser/Soller slits and the angular apertures of the axial Soller slits The presence of a monochromator in the beam path is normally accommodated by modifying the wavelength spectrum and/or by changing one or more of the axial divergence parameters Flat analyzer crystals have been incorporated into FPPF as a Lorentzian shaped angular acceptance function One of the intrinsic benefits of the fundamental parameters approach is its adaptability any laboratory diffractometer Good fits can normally be obtained over the whole 20 range without refinement using the known properties of the diffractometer, such as the slit sizes and diffractometer radius, and emission profile