Dear all, I'm new to Rietveld. I work with Powder X-ray diffraction and Fullprof.
Recently I've done a Rietveld refinement for a compound with the space group P42/nmc (n°137) and during the process I saw a quite high value of Biso of three atoms (~2.5). Then I had to refine anisotropic temperature factors of these atomic positions. As a result, two positions were well fitted, but the last one (the general position) was not. I receive the message"Matrix U non-positive definite!" in the .OUT file and then DIAMOND software showed also an error on this position. I would like to figure out the reason of this error. Can someone help me, please? Thank you a lot. P/S: The values of the anisotropic temperature factors in Ang^2 B11 = 0.01562 B22 = 0.002507 B33 = 0.000026 B12 = 0.002869 B13 = -0.001662 B23 = 0.00142 Tuong-Dan VU *Doctorante* *IMMM* (Institut des Matériaux et Molécules du Mans) UMR-6283 *Université du Maine* avenue Olivier Messiaen 72085 Le Mans Cedex 8 France Tel: 06 52 72 71 30 e-mail: * tuong_dan.vu....@univ-lemans.fr <tuong_dan.vu....@univ-lemans.fr> vutuong...@gmail.com <vutuong...@gmail.com>*
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