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Jansen J, Peschar R, Schenk H. Application of Direct Methods to powder data. A weighting scheme for intensities in the optimal symbolic addition program SIMPEL88. ACTA ACUST UNITED AC 2015. [DOI: 10.1524/zkri.1993.206.12.33] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Schenk H, van Mechelen JB, Peschar R. Real-time behaviour of crystallizing cocoa butter. Time-resolved SAXS-WAXS study. Acta Crystallogr A 2011. [DOI: 10.1107/s0108767311082936] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Schenk H, van Mechelen J, Peschar R. Structure and polymorphism of transmono-unsaturated triacylglycerols. Acta Crystallogr A 2008. [DOI: 10.1107/s0108767308087485] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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van Mechelen JB, Peschar R, Schenk H. The crystal structures of the β1and β2polymorphs of mono-unsaturated triacylglycerols and cocoa butter determined from high resolution powder diffraction data. ACTA ACUST UNITED AC 2007. [DOI: 10.1524/zksu.2007.2007.suppl_26.599] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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van Mechelen J, Peschar R, Schenk H. The fat bloom mechanism of chocolate clarified from X-ray powder diffraction data. Acta Crystallogr A 2007. [DOI: 10.1107/s0108767307099278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Dragan F, Bratu I, Borodi G, Toma M, Hernanz A, Simon S, Cristea G, Peschar R. Spectroscopic investigation of β-cyclodextrin -metoprolol tartrate inclusion complexes. J INCL PHENOM MACRO 2007. [DOI: 10.1007/s10847-007-9304-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Dova E, van Langevelde A, McKay B, Peschar R, Blomsma E. High-throughput polymorph screen of cimetidine and clarification of its nomenclature. Acta Crystallogr A 2005. [DOI: 10.1107/s0108767305085648] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Schenk H, Peschar R, Pop MM, De Ridder DJA, van Mechelen JB, Driessen RAJ. Crystal structure of chocolate from powder diffraction data. Acta Crystallogr A 2005. [DOI: 10.1107/s0108767305088082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Schenk H, Dik J, Peschar R. The production history of Naples yellow and the discoloration of the blue pigment smalt. Acta Crystallogr A 2005. [DOI: 10.1107/s0108767305079572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Brodski V, Peschar R, Schenk H. Organa– a program package for structure determination from powder diffraction data by direct-space methods. J Appl Crystallogr 2005. [DOI: 10.1107/s0021889805015876] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A new software package has been developed, namedOrgana, forab initiosolution of crystal structures from powder diffraction data by direct-space methods. The package contains energy-guiding Monte Carlo and grid-search algorithms and is based on a combined global minimization of theRfactor and a potential energy function of the system with the option of local minimization of the cost function for each generated trial structure. Basically, the potential energy function consists of van der Waals interactions, but harmonic potentials can be added to impose soft distance restraints. The program was successfully applied to the structure determination of a series of melamine phosphate compounds. The program is freely available (for all Windows platforms) from the correspondence author upon request.
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De Ridder DJA, Pop MM, van Mechelen JB, Goubitz K, Pruissen D, Driessen R, Peschar R, Schenk H. Crystal-structure determination of β′-stable triacylglycerides of the type C nC n+2C n( n= even). Acta Crystallogr A 2004. [DOI: 10.1107/s0108767304095583] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Peschar R, Pop MM, De Ridder DJA, van Mechelen JB, Driessen RAJ, Schenk H. Crystal structure of chocolate from powder diffraction data. Acta Crystallogr A 2004. [DOI: 10.1107/s0108767304095406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Tafeenko VA, Chernyshev VV, Yatsenko AV, Makarov VA, Sonneveld EJ, Peschar R, Schenk H. Intermolecular -CH(3)...O(2)N-- contacts in two polymorphic modifications of (1E)-N'-[(E)-2-cyano-1-(dimethylamino)-2-nitrovinyl]-N,N-dimethylethanimidamide. Acta Crystallogr B 2003; 59:492-7. [PMID: 12947234 DOI: 10.1107/s0108768103010231] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2003] [Accepted: 05/09/2003] [Indexed: 11/11/2022]
Abstract
The title compound was synthesized and isolated in two crystal modifications. The structure of the orthorhombic modification was determined by the X-ray powder diffraction method and the structure of the monoclinic modification was determined using the X-ray single-crystal diffraction technique. The molecules in both polymorphs are E,E isomers. Intermolecular H(3)C....NO(2) contacts and their role in the formation of the polymorphic modifications are analyzed.
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Affiliation(s)
- V A Tafeenko
- Department of Chemistry, Moscow State University, 119899 Moscow, Russia.
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Abstract
A new direct-space method forab initiosolution of crystal structures from powder diffraction data is presented. The approach consists of a combined global minimization ofRwpand the potential energy of the system. This method was tested on two organic compounds with known structure and also applied successfully in the structure determination of the previously unknown structure of melamine pyrophosphate.
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Peschar R, Brodski V, Dova E, Driessen RAJ, Goubitz K, Helmholdt RB, Van Langevelde AJ, Pop MM, Schenk H. Progress in structure determination of larger organic and organo-metallic compounds from powder diffraction data. Acta Crystallogr A 2002. [DOI: 10.1107/s0108767302086816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Dova E, Stassen AF, Nishibori E, Kato K, Peschar R, Schenk H. Temperature dependent synchrotron X-ray powder diffraction studies: Fe(II) spin crossover complexes. Acta Crystallogr A 2002. [DOI: 10.1107/s0108767302095545] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Dova E, Goubitz K, van Langevelde A, Driessen R, Mahabiersing T, Blaauw R, Peschar R, Schenk H. Structure determination of two metal-organic complexes from high-resolution synchrotron powder diffraction data. J Synchrotron Radiat 2001; 8:1186-1190. [PMID: 11679770 DOI: 10.1107/s0909049501013784] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2001] [Accepted: 08/20/2001] [Indexed: 05/23/2023]
Abstract
The crystal structures of [1,2-bis(2,6-diisopropylphenylimino)acenaphthene-N,N']carbonylchlororhodium(I) (1) and [N,N'-ethylene-bis(3-methylsalicylideneiminato)-O,N,N',O'](tetrahydrofurfuryl)-cobalt(II) (2) have been determined from high-resolution synchrotron X-ray powder diffraction data. Compound 1 is the first neutral Rh complex, in contrast with findings in the literature, containing a bidentate nitrogen ligand, and compound 2 is the first three-dimensional structure of a (five-coordinated) tetrahydrofurfurylcobalt(III) complex. Grid-search and Rietveld refinement have been used to determine and refine the structures, respectively. Crystals of 1 are orthorhombic, space group Pbca, Z = 8, with cell parameters a = 21.729 (2), b = 27.376 (3), c = 11.580 (1) A. Crystals of 2 are monoclinic, space group P2(1)/n, Z = 4, a = 16.6701 (6), b = 9.4170 (4), c = 13.7088 (7) A and beta = 96.520 (3) degrees. Chemical diagrams for the two compounds are given. Soft restraints were applied during Rietveld refinement; for 1 converging to R(p) = 8.4%, R(w) = 11.0%, GoF = 2.3, and for 2 converging to R(p) = 8.5%, R(w) = 11.4%, GoF = 7.6.
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Affiliation(s)
- E Dova
- Laboratory for Crystallography, Institute of Molecular Chemistry, Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018WV Amsterdam, The Netherlands
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Dova E, Stassen AF, Driessen RA, Sonneveld E, Goubitz K, Peschar R, Haasnoot JG, Reedijk J, Schenk H. Structure determination of the [Fe(teec)(6)](BF(4))(2) metal complex from laboratory and synchrotron X-ray powder diffraction data with grid-search techniques. Acta Crystallogr B 2001; 57:531-8. [PMID: 11468380 DOI: 10.1107/s010876810100828x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2001] [Accepted: 05/16/2001] [Indexed: 11/10/2022]
Abstract
The structure of the coordination compound [Fe(teec)(6)](BF(4))(2), hexa[1-(2-chloroethyl)tetrazole]iron(II) di(borotetrafluoride), has been determined using the grid-search techniques of the program suite MRIA. A Guinier-camera data set was used to determine the unit cell, the space group and to position the initial model. A high-resolution synchrotron powder data set was used to position a more detailed model using torsion-angle variation and to refine the structure leading to Rp = 0.0689, Rw = 0.0805 and GoF = 1.38. The crystal structure at room temperature shows the existence of two symmetry-equivalent iron(II) ions in the high-spin state.
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Affiliation(s)
- E Dova
- Laboratory for Crystallography, Institute of Molecular Chemistry, Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
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Peschar R, Israël R, Beurskens PT. The joint probability distributions of structure-factor doublets in displacive incommensurately modulated structures and their applicability to direct methods. Acta Crystallogr A 2001; 57:461-72. [PMID: 11418757 DOI: 10.1107/s0108767301003762] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2000] [Accepted: 05/01/2001] [Indexed: 11/10/2022] Open
Abstract
In 1993, alternative normalized structure factors for incommensurately modulated structures were defined [Lam, Beurskens & van Smaalen (1993). Acta Cryst. A49, 709-721]. The probability distribution associated with the structure invariants E(-H)E(H')E(H - H') has approximately the same functional form as the Cochran distribution. It was shown, however, that triplet-phase relations are relatively less reliable when satellites are involved [de Gelder, Israël, Lam, Beurskens, van Smaalen, Fu & Fan (1996). Acta Cryst. A52, 947-954]. In the present paper, an alternative approach is presented: instead of studying the distribution of a three-phase invariant, the probability distribution of the phase sum of two first-order satellite reflections (h,k,l,1 and h',k',l',-1) has been derived under the assumption that the phase of the associated main reflection (h + h',k + k',l + l',0) can be calculated from the known main (or averaged) structure. Intensive tests with randomly generated artificial structures and one real structure show a significant improvement of direct-methods phase-sum statistics. Functional similarities with conventional direct methods, employing normalized structure factors and the Cochran distribution, are discussed.
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Affiliation(s)
- R Peschar
- Laboratory for Crystallography, Institute of Molecular Chemistry, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands
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van Langevelde A, Peschar R, Schenk H. Structure of beta-trimyristin and beta-tristearin from high-resolution X-ray powder diffraction data. Acta Crystallogr B 2001; 57:372-7. [PMID: 11373397 DOI: 10.1107/s0108768100019121] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2000] [Accepted: 11/29/2000] [Indexed: 11/10/2022]
Abstract
The crystal structures of beta-1,2,3-tritetradecanoylglycerol (beta-trimyristin or beta-MMM) and beta-1,2,3-trioctadecanoylglycerol (beta-tristearin or beta-SSS) have been determined from high-resolution synchrotron X-ray powder diffraction data. Grid search and Rietveld refinement have been used to determine and refine the structure, respectively. Both substances crystallize in space group P1; with Z = 2. The unit-cell parameters for beta-MMM are a = 12.0626 (6), b = 41.714 (1), c = 5.4588 (3) A, alpha = 73.388 (4), beta = 100.408 (5) and gamma = 118.274 (4) degrees. For beta-SSS the unit-cell parameters are a = 12.0053 (7), b = 51.902 (2), c = 5.4450 (3) A, alpha = 73.752 (5), beta = 100.256 (6) and gamma = 117.691 (5) degrees. Soft-distance restraints have been applied to the molecules during refinement. For beta-MMM the final R(p) value obtained is 0.053 and for beta-SSS the final R(p) value is 0.041.
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Affiliation(s)
- A van Langevelde
- Laboratory for Crystallography, Institute of Molecular Chemistry (IMC), Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands
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Van Langevelde A, Van Malssen K, Driessen R, Goubitz K, Hollander F, Peschar R, Zwart P, Schenk H. Structure of CnCn+2Cn-type (n = even) beta'-triacylglycerols. Acta Crystallogr B 2000; 56 ( Pt 6):1103-11. [PMID: 11099979 DOI: 10.1107/s0108768100009927] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2000] [Accepted: 07/17/2000] [Indexed: 11/11/2022]
Abstract
The crystal structures of the beta' phase of CLC (1, 3-didecanoyl-2-dodecanoylglycerol) and MPM (1, 3-ditetradecanoyl-2-hexadecanoylglycerol) have been determined from single-crystal X-ray diffraction and high-resolution X-ray powder diffraction data, respectively. Both these crystals are orthorhombic with space group Iba2 and Z = 8. The unit-cell parameters of beta'-CLC are a = 57.368 (6), b = 22.783 (2) and c = 5.6945 (6) A and the final R value is 0.175. The unit-cell parameters of beta'-MPM are a = 76.21 (4), b = 22.63 (1) and c = 5.673 (2) A and the final R(p) value is 0.057. Both the beta'-CLC and beta'-MPM molecules are crystallized in a chair conformation, having a bend at the glycerol moiety. The zigzag planes of the acyl chains are orthogonally packed, as is typical for a beta' phase. Furthermore, unit-cell parameters of some other members of the C(n)C(n+2)C(n)-type triacylglycerol series have been refined on their high-resolution X-ray powder diffraction pattern. Finally, the crystal structures are compared with the currently known structures and models of triacylglycerols.
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Affiliation(s)
- A Van Langevelde
- Laboratory for Crystallography, Institute for Molecular Chemistry (IMC), Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
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Lasocha W, Peschar R, Jansen J, Schenk H. Crystal structures from powder data by direct methods. Acta Crystallogr A 1996. [DOI: 10.1107/s0108767396096985] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Seljee FR, Peschar R, Schenk H. SIMPROT: a program in development for crystal structure determination of proteins. Acta Crystallogr A 1996. [DOI: 10.1107/s0108767396096705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Schenk H, van Malssen KF, Peschar R. Real-time X-ray powder diffraction experiments on cocoa butter. Acta Crystallogr A 1996. [DOI: 10.1107/s0108767396083535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Peschar R. Joint probability distributions of structure factors in case of incommensurately displacive modulations. Acta Crystallogr A 1996. [DOI: 10.1107/s0108767396096882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Kyriakidis CE, Peschar R, Schenk H. The Estimation of Four-Phase Structure Invariants Using the Single Difference of Isomorphous Structure Factors. Acta Crystallogr A 1996. [DOI: 10.1107/s0108767395011226] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023] Open
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Peschar R, Schenk H, Čapková P. Preferred-Orientation Correction and Normalization Procedure forAb InitioStructure Determination from Powder Data. J Appl Crystallogr 1995. [DOI: 10.1107/s0021889894010629] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Spengler R, Zimmermann H, Burzlaff H, Jansen J, Peschar R, Schenk H. Ab initio structure determination from powder data using direct methods. Acta Crystallogr B Struct Sci 1994. [DOI: 10.1107/s010876819400306x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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van Malssen K, Peschar R, Schenk H. Geometrical aspects of real-time powder diffraction using a normal generator and a linear diode-array detector. J Appl Crystallogr 1994. [DOI: 10.1107/s0021889893009823] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Schenk H, Jansen J, Capkova P, Lasocha W, Rafaja D, Peschar R. Direct methods for powder diffraction. Acta Crystallogr A 1993. [DOI: 10.1107/s0108767378098967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Kyriakidis C, Peschar R, Schenk H. Incorporation of direct methods with all the protein-crystallography phasing tools available. A new probabilistic expression for triplets and quartets. Acta Crystallogr A 1993. [DOI: 10.1107/s0108767378099171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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Wang YF, Peschar R, Schenk H. The use of a modified double Patterson function in direct phase determination. Acta Crystallogr A 1993. [DOI: 10.1107/s0108767378098487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Peschar R, Schenk H, Capkova P. Texture correction of powder data for ab initiostructure determination. Acta Crystallogr A 1993. [DOI: 10.1107/s0108767378098992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Čapková P, Peschar R, Schenk H. Partial multiplicity factors for texture correction of cubic structures in the disc-shaped crystallite model. J Appl Crystallogr 1993. [DOI: 10.1107/s0021889893000810] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Kyriakidis CE, Peschar R, Schenk H. On direct-methods phase information from differences between isomorphous structure factors. Acta Crystallogr A 1993. [DOI: 10.1107/s0108767392011632] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Kyriakidis CE, Peschar R, Schenk H. On the relation between the diffraction ratio, the doublet values and the reliability of the triplet estimates. Acta Crystallogr A 1993. [DOI: 10.1107/s0108767392009863] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Jansen J, Peschar R, Schenk H. On the determination of accurate intensities from powder diffraction data. II. Estimation of intensities of overlapping reflections. J Appl Crystallogr 1992. [DOI: 10.1107/s0021889891012128] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Even the best least-squares algorithm to extract intensities from a powder diagram will not be able to determine the separate intensities of completely overlapping peaks. In this paper a new method (DOREES) is presented to determine these intensities more accurately by applying relations between structure factors derived from direct methods and the Patterson function. The intensities obtained from the least-squares fit are used as a starting set for DOREES. Comparative tests on both artificially generated and real data show that DOREES improves the intensity set considerably.
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Jansen J, Peschar R, Schenk H. On the determination of accurate intensities from powder diffraction data. I. Whole-pattern fitting with a least-squares procedure. J Appl Crystallogr 1992. [DOI: 10.1107/s0021889891012104] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
A new algorithm, direct intensity fitting, has been developed which performs a whole-pattern fitting for powder data. The algorithm is related to the fitting technique of Pawley [J. Appl. Cryst.
14, 357–361] but does not require start values for the intensities of the individual reflections. Comparative tests show that direct intensity fitting extracts more accurate intensities from a powder diffractogram and reduces the minimum peak distance for accurate data to half of the half-widths. The structure of the superconductor Ba2YCu3O8−x
can be solved in a default direct-methods run with direct-intensity-fitting intensities extracted from a normal laboratory powder diffractogram.
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Kronenburg MJ, Peschar R, Schenk H. Derivation of exponential joint probability distributions of structure factors in P1 with maximum entropy and irreducible cluster integrals. Acta Crystallogr A 1991. [DOI: 10.1107/s0108767391004634] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023] Open
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Peschar R, Schenk H. The joint probability distribution of structure factors incorporating anomalous-scattering and isomorphous-replacement data. Acta Crystallogr A 1991. [DOI: 10.1107/s0108767391002441] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Schenk H, Peschar R. Optimal symbolic addition. Acta Crystallogr A 1987. [DOI: 10.1107/s0108767387078012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Peschar R, Schenk H. Computer-aided derivation of theoretical joint probability distributions of normalized structure factors. Acta Crystallogr A 1987. [DOI: 10.1107/s0108767387099094] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Peschar R, Schenk H. Estimation of quartet phase sums from a new joint probability distribution of normalized structure factors. Acta Crystallogr A 1987. [DOI: 10.1107/s0108767387099823] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Peschar R, Schenk H. Estimating invariant phase sums from a new joint probability distribution of structure factors. Acta Crystallogr A 1984. [DOI: 10.1107/s0108767384087444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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