It all depends on the definition. If/when we agree on the definition, there is usually no points for further arguing. Anyway we could call Relieved method a structure determination from powder data as long as it does not included solving structure (or as David elegantly put - true structural solution). Peter .................................................................... Peter Y. Zavalij Director - X-ray Crystallographic Center University of Maryland, College Park, MD 20742
On Wed, Aug 29, 2018 at 12:38 PM David Elbert <elb...@jhu.edu> wrote: > Absolutely important that people understand that the Rietveld method is > structure refinement and not solution, but as Larry points out sometimes > you can get a more out of it if you’re clever… and have no other choice! > Here’s a second example: > > Stubbs et al., 2010, Uranyl phosphate sheet reconstruction during > dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H2O], American > Mineralogist 95 (8-9): 1132-1140 which is a bit of a brute-force approach > to implying structures of some uranyl phosphates in a synchrotron heating > experiment. Joanne Stubbs sorted through known structures of related > materials and used observed trends in refinements to select similar > structures to further investigate. Able to then postulate reasonable > structures which then refined to the observed data and provided insight > into this interesting group of materials. > > Not the standard way to employment of Rietveld Refinement and certainly > not true structural solutions, but a smart, useful, and rather satisfying > application nonetheless. > > Best- > David > > David Elbert > Hopkins Extreme Materials Institute > Malone Hall > Johns Hopkins University > 3400 N. Charles St > Baltimore, MD 21218 > > (410) 516-5049 > > elb...@jhu.edu > > > > > > > > > On Aug 29, 2018, at 12:09 PM, Larry Finger <larry.fin...@lwfinger.net> > wrote: > > On 08/29/2018 04:15 AM, Le Bail Armel wrote: > > Hi, > After the IUCr Monograph on Crystallography 13 (2002) > entitled "Stucture Determination from Powder Diffraction Data" > you may find in the preface : > "Although the Rietveld method of structure refinement from powder > diffraction data is often loosely considered to be synonymous with > structure > determination, it is not. The Rietveld method only comes into play in the > final stage of the structure solution process when an approximate > structural > model has been found." > WIF David, K Shankland, LB McCusker, C Baerlocher > A clear distinction having my complete agreement. > Armel > > > Armel, > > Although the above statement may be generally true, I can provide a > counter example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and > Robert E. Dinnabier, "Synthesis, crystal structure, and phase relations of > AlSiO2OH, a high pressure hydrous phase", American Mineralogist, V. 83, > 881-888, 1998, we only had a powder - no single crystals. From data > measured at ESRF, we used GSAS to isolate the peaks of interest for the > unknown phase, and used program TREOR to autoindex the unknown and identify > the impurity phases. We then extracted intensities using the LeBail method, > and determined the structure using direct methods with program SIRPOW. The > structure was then refined with GSAS. We were even able to locate the H > atom from Fourier maps! > > Even 20 years ago, it was possible to determine the structure from X-ray > powder patterns. > > Larry > > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list <alan.he...@neutronoptics.com > > > Send commands to <lists...@ill.fr> eg: HELP as the subject with no body > text > The Rietveld_L list archive is on > http://www.mail-archive.com/rietveld_l@ill.fr/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list <alan.he...@neutronoptics.com > > > Send commands to <lists...@ill.fr> eg: HELP as the subject with no body > text > The Rietveld_L list archive is on > http://www.mail-archive.com/rietveld_l@ill.fr/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > >
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
