[sdpd] GSAS: RF2 ?

[Marco Sommariva <marco.sommariva...@mater.unimib.it>]

Dear GSAS users,
first of all Good Easter to everybody (even if quite late!).

I have a problem with GSAS: I don't understand why, during a refinement
of a TOF neutron profile, I see a big increase of the Bragg index RF^2
(from 12% to 61% !!)  if I insert in the refinement just three little
peaks (i.e. if I start my histogram from 0.67 instead from 0.7
Angstrom). Profile indexes Rp and wRp remains the same, as these 3 peaks
are well fitted by the tetragonal symmetry chosen !! So they don't
belong to an impurity, and space group seems right!
I don't have many peaks, so I would like to use also these peaks in the
refinement.

Another little question: which convergence criterion do you think it's
better for a normal Rietveld refinement? In Expgui the default value is
fixed to 0.01, but I read it could be bigger but less than 0.10.

Thanks a lot in advance, 
marco



-- 
Marco Sommariva
Department of Materials Science
University of Milano - Bicocca
Via R. Cozzi 53 - 20125 MILAN, ITALY
Phone +39.02.6448.5141 (5142)
Fax   +39.02.6448.5400
e-mail: marco.sommariva...@mater.unimib.it





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