RE: Sequence for varying parameters in FullProf
> You might want to have a read of this paper... Or else you could read the Fullprof manual :-) on http://www.ill.eu/sites/fullprof/php/tutorials.html in particular the chapter on "The Rietveld Method in Practice" which is good advice whatever Rietveld program you use. To quote: " Use the best possible starting model: this can be easily done for background parameters and lattice constants. In some cases, in particular when the structural model is very crude, it is advisable to analyse first the pattern with the profile matching method in order to determine accurately the profile shape function, background and cell parameters before running the Rietveld method. Do not start by refining all structural parameters at the same time. Some of them affect strongly the residuals (they must be refined first) while others produce only little improvement and should be held fixed till the latest stages of the analysis. Before you start, collect all the information available both on your sample (approximate cell parameters and atomic positions) and on the diffractometer and experimental conditions of the data measurement: zero-shift and resolution function of the instrument, for instance. Then a sensible sequence of refinement of a crystal structure is the following: 1. Scale factor. 2. Scale factor, zero point of detector , 1rst background parameter and lattice constants. In case of very sloppy background, it may be wise to actually refine at least two background parameters, or better fix the background using linear interpolation between a set of fixed points provided by user. 3. Add the refinement of atomic positions and (eventually) an overall Debye-Waller factor, especially for high temperature data. 4. Add the peak shape and asymmetry parameters. 5. Add atom occupancies (if required). 6. Turn the overall temperature factor into individual isotropic thermal parameters. 7. Include additional background parameters (if background is refined). 8. Refine the individual anisotropic thermal parameters if the quality of the data is good enough. 9. In case of constant wavelength data, the parameters Sycos and/or Sysin to correct for instrumental or physical aberrations with a COS or SIN angular dependence. 2θ 10. Microstructural parameters: size and strain effects. In all cases, it is essential to plot frequently the observed and experimental patterns. The examination of the difference pattern is a quick and efficient method to detect blunders in the model or in the input file controlling the refinement process." __ Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE <[EMAIL PROTECTED]> +33.476.98.41.68 http://www.NeutronOptics.com/hewat __
Re: Sequence for varying parameters in FullProf
Also FullProf manual (comes with the program) gives suggestions about the sequence. -Markus -- Markus Valkeapaa Department of Chemistry Helsinki University of Technology P.O. Box 6100, FI-02150 TKK Office B206 tel. +358 9 451 2596, +358 44 290 2515 fax. +358 9 462 373 email [EMAIL PROTECTED] -- Palash Manna kirjoitti: Hi all, I am a newcommer in this field. Recently, I have started refining X-ray and Neutron data of Perovskite material using FullProf. I would like to know about the sequence for varying different parameters (like Biso, Bov, a, b, c, scale, zero shift, etc) and also, the logic behind the sequence. Thanks in advance and regards,
RE: Sequence for varying parameters in FullProf
You might want to have a read of this paper: McCusker, L. B., Von Dreele, R. B., Cox, D. E., Louër, D. & Scardi, P. 1999, 'Rietveld Refinement Guidelines', Journal of Applied Crystallography, vol. 32, no. 1, pp. 36-50. Cheers Matthew Matthew Rowles CSIRO Minerals Box 312 Clayton South, Victoria AUSTRALIA 3169 Ph: +61 3 9545 8892 Fax: +61 3 9562 8919 (site) Email: [EMAIL PROTECTED] -Original Message- From: Palash Manna [mailto:[EMAIL PROTECTED] Sent: Tuesday, 27 May 2008 14:16 To: rietveld_l@ill.fr Subject: Sequence for varying parameters in FullProf Hi all, I am a newcommer in this field. Recently, I have started refining X-ray and Neutron data of Perovskite material using FullProf. I would like to know about the sequence for varying different parameters (like Biso, Bov, a, b, c, scale, zero shift, etc) and also, the logic behind the sequence. Thanks in advance and regards, -- Mr. Palash Kumar Manna Junior Research Fellow, Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085
