International
Tables for Crystallography Volume H Powder diffraction Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk © International Union of Crystallography 2018 |
International Tables for Crystallography (2018). Vol. H, ch. 3.4, pp. 276-277
Section 3.4.4.2. Evolved indexing programs^{a}Institute of Crystallography – CNR, Via Amendola 122/o, Bari, I-70126, Italy |
Implemented in the EXPO program (Altomare et al., 2013) to perform the powder pattern indexing step, N-TREOR09 is an update of N-TREOR (Altomare et al., 2000), which in turn is an evolution of TREOR90, and preserves the main strategies with some changes introduced to make the program more exhaustive and powerful. In particular:
This program is also able to index powder patterns from small proteins: see Example 4 in Section 3.4.4.6.2.
The most recent of a series of versions, DICVOL14 is the successor of DICVOL04 (Boultif & Louër, 2004) and DICVOL06. DICVOL06 includes DICVOL04 with its optimized search procedure and an extended search in shells of volumes. DICVOL04 represented an improvement of DICVOL91. Among the features of DICVOL06 are:
No formal limits on the number of input Bragg peaks have been established but, for reliable indexing, it is recommended that 20 or more peaks (in the low-2θ region) are used.
Compared to DICVOL04/DICVOL06, DICVOL14 includes: an optimization of filters in the final stages of the convergence of the successive dichotomy process; an optimization and extension of scanning limits for the triclinic case; a new approach for zero-point offset evaluation; a detailed review of the input data from the resulting unit cells; and cell centring tests. DICVOL14 has been improved particularly for triclinic cases, which are generally the most difficult to solve with the dichotomy algorithm.
References
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