Advances in powder diffraction pattern indexing:N-TREOR09

Abstract

Powder pattern indexing can still be a challenge, despite the great recent advances in theoretical approaches, computer speed and experimental devices. More plausible unit cells, belonging to different crystal systems, are frequently found by the indexing programs, and recognition of the correct one may not be trivial. The task is, however, of extreme importance: in case of failure a lot of effort and computing time may be wasted. The classical figures of merit for estimating the unit‐cell reliability {i.e.M20 [de Wolff (1968). J. Appl. Cryst.1, 108–113] and FN [Smith & Snyder (1979). J. Appl. Cryst.12, 60–65]} sometimes fail. For this reason, a new figure of merit has been introduced in N‐TREOR09, the updated version of the indexing package N‐TREOR [Altomare, Giacovazzo, Guagliardi, Moliterni, Rizzi & Werner (2000). J. Appl. Cryst. 33, 1180–1186], combining the information supplied by M20 with additional parameters such as the number of unindexed lines, the degree of overlap in the pattern (the so‐called number of statistically independent observations), the symmetry deriving from the automatic evaluation of the extinction group, and the agreement between the calculated and observed profiles. The use of the new parameters requires a dramatic modification of the procedures used worldwide: in the approach presented here, extinction symbol and unit‐cell determination are simultaneously estimated. N‐TREOR09 benefits also from an improved indexing procedure in the triclinic system and has been integrated into EXPO2009, the updated version of EXPO2004 [Altomare, Caliandro, Camalli, Cuocci, Giacovazzo, Moliterni & Rizzi (2004). J. Appl. Cryst. 37, 1025–1028]. The application of the new procedure to a large set of test structures is described.

Thermally induced polymerization of binuclear [Ni2(en)2(H2O)6(pyr)]·4H2O complex

“…Indexing of powder XRD peaks and space group determination was performed using Jana2006 [27], and N-TREOR09 program [28] implemented in EXPO 2013 package. Rietveld analysis of X-ray powder diffraction data was done using GSAS-II program package [29], with literature data for initial parameters, using pseudo-Voigt functions and Chebyshev function as a background.…”

Thermal, Spectroscopic, and Ab Initio Structural Characterization of Carprofen Polymorphs

“…The result of the silicon refinement has given for the wavelenght of 0.799980 ± 0.000131 Å. Indexing of the SR-XRPD diffraction patterns was performed using EXPO2009 program. 23 Pawley refinement, structure solution, and Rietveld refinement were, instead, performed using TOPAS V3.0 software (Bruker AXS, Karlsruhe, Germany). 24 A model of the carprofen molecule was generated, using density functional theory (DFT) in the gas phase (vide infra).…”

Reversed de Wolff figure of merit and its application to powder indexing solutions

“…However, the de Wolff figure of merit appears to be superior in efficacy, as supported by other authors (e.g. Wu, 1988;Altomare et al, 2009). Various figures of merit have been proposed by Taupin (1988), Bergmann (2007), Le Bail (2008), Altomare et al (2009) and so on.…”

“…Wu, 1988;Altomare et al, 2009). Various figures of merit have been proposed by Taupin (1988), Bergmann (2007), Le Bail (2008), Altomare et al (2009) and so on. In the latter two cases, the value of the R factor R p obtained as a result of intensity extraction is used for the figure of merit.…”